Thanks - these are about 1/8" pop-up pistons, not domes, as I'm guessing based on other info I'm reading. Not yet having a chance to cc the piston pop-up and "do the math" via that formula yet, and based on approximate ratios for 350 flattops and 64cc vortec heads, my semi-educated guess is that I'd probably want to go with a 76cc head, to avoid detonation. We'll see later how that works out on paper. Right now I'm trying to decide whether to keep the main bearings I have or buy a new set, also trying to find info on whether or not I need some sort of gasket for the oil filter conversion kit (from canister to screw-on). If so, will PermaTex suffice?