1) Will converting my circuit to match the
     AB763 SR layout do the trick or are there
     any tricks/common mistakes that I should
     be aware of?

As long as the component values all match those in the
AB763 circuit and your lead dress is decent, you should
nail the blackface sound. Don't forget to change some
components in the phase inverter circuit. Replace the
two 47K plate load resistors with 82K/100K; replace
the two 330K grid load resistors with 1Meg, and
replace the .01 input cap with .001.
 

     2) What about the output transformer? I'm
     planning to use the amp with a 4 ohm load
     for which it was designed. I've heard that
     the bandmaster reverb output transformer
     is not the best sounding... would it be worth
     getting a different one?

It depends upon what you're looking for. The stock OT
is not BAD sounding, but it is smaller than than the
stock OT in a Super Reverb or Bassman head. The
smaller OT will definitely saturate earlier, especially in
the bass frequency range. If you want maximum loud
and clean, then go for a larger OT (I recommend
getting one with multiple impedance taps, in case you
decide later to use a different speaker cab). If you like
some compression and overdrive, then you might be
perfectly happy with the stock OT.
 

     Any other tips or advice would be
     appreciated as well. 

Make sure ALL the electrolytic caps get replaced,
including the bias filter cap and the cathode bypass caps
in the preamp section.

When replacing the filter caps , replace the two main
80uf with two 220uf at 350vdc this will help carry the
low end better. Also replace that stock OT with a
bassman reissue trannie for a louder clean sound. Ive
done these mods before and they work great. Its a
standard for me to use the 220uf in regular mid 60s
bassman heads for better low end clarity without flab.
Also upgrade your resitors to carbon film as they will
last much longer than the old carbon comp. Some
people say there is a difference in sound between these
two types of resistors but most musicians I know can't
tell the difference in any tone change. or you can use
flame proof if you like but carbon film is fine. Replace
the 100k resistors that feed the preamp plates with 1
watt resistors too. I hope this helps, Im sure some of
the other guys will chime in here with some more juicy
stuff to do.