You did say "any ideas"... 
 
How about an 8417? They are showing up pretty regularly on
eBay. You should get a little more clean headroom plus greater
overdrive capability when cranked - a pretty rare combination
IME. As Dan pointed out, heater draw is higher (1.6 A for this
tube) so watch your heater voltage, and you will have to change
your cathode resistor for sure...
 
but you said "without modification"? 
 
Ray