If you are gonna put the 72cc heads on a 455 you could go with a 15 cc or so Keith Black dished piston and get the cc's back up to 87cc or so. Then you can run pump gas and it'll still snap your neck back at will. And Butler even has 'em !!(half way down this page) http://www.jbp-pontiac.com/products/rods_pistons_pins/pistons.html