You might check out the 318 piston offerings from www.hughesengines.com. I would strive for .035-.040" quench which would be doable with those closed chambered heads. Being cube limited you need all the torque you can muster & quench will let you run a higher CR along with a good curve on a particular fuel for more power. I'd suggest a 1.88 intake & some bowl hogging/mild porting to clean things up a bit. Google the 302's as there's some good info out there on them just depends on how much time(& money) you want to invest