1) input jack resistor values: The 68k/1 meg setup is probably
about as good as you're going to get here.

2) Plate load resistors: Changing the plate load from say 100k to
220k is going to reduce the tube current somewhat and give you a
little more negative bias. This is actually going to make the stage run
cleaner but the net gain will increase. This can allow you to hit the
driver a little harder.

3) Cathode resistors: Decreasing the size of the cathode resistor is
going to give you more current through the tube and thus a little less
headroom. Because this resistor is typically bypassed with a cap
you won't see any substantial gain increase in the stage. You may
also run the risk of having the amp fart out on you.

4) Other suggestions: 
One easier way to get a whopping gain increase is to move the tone
stack from after the first gain stage to after the second stage. This is
pretty easy to do in a Fender by just swapping the stages that the
volume pot goes to. For a few ideas along these lines go to Steve
A's site, http://www.techaccessinc.com/blueguitar/ and check out
the schematic of the Blues Junior.

You can also try knocking back the grid resistors to the power
tubes from 220k to about 100k. This has several effects. First, it
changes the time constant of the RC network and gives you a little
faster response. Second, the gain of the driver will be reduced
letting you drive the driver a little harder( sheesh, now that's
reduntant for you!) before you start to clip the power tubes.

Last suggestion; play around with the feedback network a little. I
emphasize the word little here! You can easily turn the power amp
into an oscillating nightmare if you get too wild with the changes. I'd
suggest starting by changing the 820 ohm feedback resistor to
something in the neighborhood of 33k. Temporarily wiring in a 50k
pot as a rheostat here until you find a value that you like is a lot
easier than swapping resistors in and out.

Hope these suggestions point you in the right direction.

1) input jack resistor values: The 68k/1 meg
     setup is probably about as good as you're
     going to get here.

Maybe, but there are some subtle tweaks here that can make
a flat guitar pickup sound better or an overly hot pickup work
better with farty sounding Fender amps. 

     2) Plate load resistors: Changing the plate
     load from say 100k to 220k is going to
     reduce the tube current somewhat and give
     you a little more negative bias. This is
     actually going to make the stage run cleaner
     but the net gain will increase. This can allow
     you to hit the driver a little harder.

You'll have to explain this one a little better Carl. 
I agree with parts but, that isn't "quite" what my experience
has been... :>)

     3) Cathode resistors: Decreasing the size of
     the cathode resistor is going to give you more
     current through the tube and thus a little less
     headroom. Because this resistor is typically
     bypassed with a cap you won't see any
     substantial gain increase in the stage. You
     may also run the risk of having the amp fart
     out on you.

Too a point, but when the current through the cathode resistor
is enough to drop the plate voltage to a value that is bit higher
then half of the B+ applied, I think you'll find that is where the
tube is actually the sweetest and still has excellent headroom.
I prefer to keep the "standard" 12AX7 tridode ideling around
1ma to 1.2ma using other parameter values like, Ep=200vdc
with an Rp of about 91K to 120K, Rk 1K to 1K5 and Ck of
about 10uF to 22uF.
Keep in mind, the 12AX7 triodes are normally used as class
A amps and need the proper bias, current and plate voltage to
keep them running in their linear curve with the max amount of
gain desired.

     4) Other suggestions: 
     One easier way to get a whopping gain
     increase is to move the tone stack from after
     the first gain stage to after the second stage.
     This is pretty easy to do in a Fender by just
     swapping the stages that the volume pot goes
     to. For a few ideas along these lines go to
     Steve A's site,
     http://www.techaccessinc.com/blueguitar/
     and check out the schematic of the Blues
     Junior.

True, the typical Fender tone stack, shoved in between the
two halves of a 12AX7, does use up quite a bit of signal.
But I think it has the best bang for the buck in terms of overall
tonal effect vs cost, parts count and ease of construction, and
as long as the next triode stage has good gain... (called the
tone recovery stage for a reason)... it works wonderfully right
where it is. 
There are other places you can get more drive, if you want or
need it, other then shifting the tone stack to after the traditional
tones stack recovery section.
Maybe Randall A. can add something here too.
I know Randall has a particular interest in low Zed cathode
driven tone stacks and the effect they have on the driver. 

     You can also try knocking back the grid
     resistors to the power tubes from 220k to
     about 100k. This has several effects. First, it
     changes the time constant of the RC network
     and gives you a little faster response. Second,
     the gain of the driver will be reduced letting
     you drive the driver a little harder( sheesh,
     now that's reduntant for you!) before you
     start to clip the power tubes.

I agree!
This is a good mod for many Fender amps that can benifit
from some additional preamp "tone" before the power tube
fart out.
But, this is not quite so when using cathode biased power
tubes.
And dropping the coupling caps value a notch or so, from say,
.1uF tp .047uF to even .033uF, can go a long way in
controlling the woofie nasties too.

     Last suggestion; play around with the
     feedback network a little. I emphasize the
     word little here! You can easily turn the
     power amp into an oscillating nightmare if
     you get too wild with the changes. I'd suggest
     starting by changing the 820 ohm feedback
     resistor to something in the neighborhood of
     33k. Temporarily wiring in a 50k pot as a
     rheostat here until you find a value that you
     like is a lot easier than swapping resistors in
     and out.

I agree again!
Changing the feedback loop voltage lower by a slight amount,
but staying reasonable, is a great way to get a more "fun"
sounding amp.
It will really loosen things up.
But, going from 820ohms to 33K-50K , is too much for me in
an otherwise normal good sounding Fender amp.
OK if you play only mournfully bluesy slide guitar...
Did I say woofie?
Use small incremental amounts when doing this or use a small
25k-50k trimpot in place of the 820 ohm resistor on the
eyelet board.
You'll HAVE to go back to the PI/driver and shut it down a
little or into the preamp stages and reduce their outputs a a bit
here and there to get really good results if you try and use
somethng as large as 33K to 50K.
Personally, when playing at any decent volume, without
redoing the PI/driver, I don't like the sound at all when using
anything past about 3K for the FB resistor.
You can also yank off the grounded 47 to 100 ohm resistor 
and use a 200ohm to 500ohm 1/2w resistor.
By using a 500ohm to 1K resistor you can bypass it with a
.22uF to 1uF cap to get a cranked with presence control
sound too.

I think the biggest problem I see with using a 220K plate load
resistor, is that if the cathode bias resistor is too low there will be a
MUCH larger voltage drop across the plate load resistor and the
headroom will probably be reduced, not increased.
Typically, you might have a proper triode setup with a 220K plate
load and a much larger Rk then you're use to seeing.
This limits the current and the voltage drop.
The tiny little signals an average guitar pickup puts out, would
hardly have any effect on driving the tube out of it's linear curve or
out of class A.

    " With the volume maxed a strat will give you a
     little over a volt but by then you'll have power
     amp clipping."

Did you mean out of the pickup, or AC out of the plate?
My best sounding amps never have first preamp sections that
output more then a few volts of AC. 

     "On the feedback loop I like the sound of 22k/4.7k
     combination. To me it's a nice compromise."

OH...OK!
I didn't see where you mentioned you were upping the grounded
resistor by a factor of 47!!! 
That makes a big difference, doesn't it? :>)
22K/4K7...Check that ratio of 4.7:1, an average Marshall using a
56K and 2K5 presence control (abt 22.5:1), 100K and a 2K5
Presence control (40:1) and the stock Fender of abt 8.1 and you
can see where your choice of the 4.7:1 lies.

     "You could also bypass the 22k with a small cap of
     around 250p but I'm not a big fan of that. seems
     to roll of too many highs."


Hmmm...I not sure you'd hear the 250P cap across the 22K FB
resistor.
The -3dB point would be about 29KHz. 
It might be OK for a little ultra high freq oscillation control though.
But it also might start one!
If you wanted a bass or mid boost (FB high or mid cut), the idea
discussed hear frequently of using a big resistance in the FB loop,
and then bypassing it with a small cap, is pretty cool, and to a
point, works well.
But, when using such a small 22K FB resistor, I think you'd do
better to try something like bigger, like a .0022uF to .0047uF cap,
and, if you were looking for a big boomey bottom, using a 22K FB
resistor, I think you'd have to go way up there like around .022uF!
By that time you may as well not have any FB voltage!
Resonant FB loops are tricky and can create horrible PI/driver
distortions and oscillations when the amp is cranked and there's a
chance it will be driven to clipping! 

     anway, to make a long story short here's what I
     like to do to my Fenders....


    " 1) change the input grid stoppers to 33k"


If by that you mean the top 68K resistor, as seen in the scheamtic
drawings, OK. But not both 68Ks replaced with 33K, right?
I prefer to use a 22K-33K and the 68K on the middle resistor, and
then move to the tube socket and install a small 1/4w to 1/2 watt
20K to 33K on the tube socket's grid lug.

    " 2) change the cathode bypass caps to 5uF."

I like this too... I use a bunch of 5uFs and 10uFs.
The -3dB point of a 12AX7 with a 100K plate load resistor, a
1K5 Rk and a 5uF Ck is about 40Hz... 10uF is about 20Hz. 

     "3) change the power tube grid resistors to 100k
     and the grid stoppers to 4.7k"


I tend to drop these too.
Sometimes as low as 100K... it depends on if the amp is cathode
biased or fixed bias and what amp it is and also what year it is too.
Grid stoppers can be about anything up to 33K to 47K with nearly
no difference in sizzle tone to my old man ears.

     "4) change the driver coupling caps to 0.047uF"


I'm OK with that too and think, for fun, everyone should
experiment with going down to .022uF and back up to .1uF.

     "5) change the driver input cap to 0.01uF"


Oops... it depends on the amp because, you'll start getting into
murky waters if you over do it... I wish I had a dollar for every
"Torres" modded amp I've pulled the stupid .022uF coupling cap
off!
Sure it sounds great at low bedroom volumes but wait until you go
out and play it louder and with a bass player. Woof!
I usually find, for my taste, most blackface or silverface Fenders
need nothing higher then .0068uF, if the rest of the amp is set up
properly and in balance. 
Your choice of .01uF is still pretty close to that and should work
fine if the other stuff is addressed too.
This is a pretty important cap and I'm always surprised to see so
many cheap ceramic .02uF caps in Fender amps here.
Some of the best, killer sounding Fender amps I've worked on had
small, cheap chicklet sized poly whatever plastic PI/driver coupling
caps!

     "6) change the feedback loop values to 22k/4.7k"


I guess I already replied to this....22k/4.7= abt 4.7:1 ratio... stock
Fender 820\100= about 8:1 ratio. blah blah...

     "7) add a 120pF cap across the plates of the driver
     to supress oscillation. (good insurance if you don't
     have a scope)"


No guarantee it will stop all oscillations, but I always make sure
there is some snubber cap in there too.
I've tried everything from 47pF to 470pF and I can't really hear
anything bad happening with the 470pF caps so it looks like for the
most part, anything works in that range.

     "Feel free to comment...I'm always open to new
     ideas"

Me too... I'm considered by many to be a pretty big bag of hot air
but I'm always learning new things from a variety of different
sources and willing to be "corrected" :>)