First thing you should do is ditch the heads.
Look for a set of "049", or "781" castings. These were early to mid 70s issue and are easy to draw 500hp out of.
I have a 1973 454 with 049 heads, Sealed Power H426P pistons, Holley Strip Dominator intake, a mild Crane street solid lifter, flat tappet cam, and Holley 4160 750cfm carb. I'm in the 500hp range and it will turn 7,000rpm all day long.
My 049s have had 2.19/1.88 valves with pocket porting, and gasket match.
The 049/781 oval port heads flow well enough to give good HP numbers and still maintain the low end torque we need to get these heavy pick up trucks moving.