Heads
Don't WASTE your time, or $$$ on those heads for that C.I. and C/R At best fully ported you will see 400 to 420 CFM. You need a head that will flow 470 CFM to make your short block start to work!
You have entered the world of 18, 14, and 11, degree heads. Shaft rockers, sheet metal intakes, and carbs that flow 1350 + CFM. Lots of $$$ and maintanance to make it run. This is what it takes to get the H.P. #s from this kind of C.I.
Do your motor a favor and SELL those heads! They are not made for that kind of C.I. Yes they will work, but not worth putting on!
What cam, intake, and carb are you planning on putting on this short block?