500 HP will be easy.get the heads figured first.Im not a big fan of hydraulic flat tappet,but they work well to 6,000 rpm.They tend to have a lumpy sounding idle way above the performance they offer.
I didnt ask,is it a 3/8 " rod bolt or 7/16s? if 3/8s for sure replace bolts. do a basic blue printing job on the engine,deck/square/align hone the block, 9 1/2 CR for iron heads,maybe 10 1/4 for aluminum, open plenum intake ( vic Jr oval port),850 cfm carb, decent headers. thats all it takes to get 500 hp from 460 cubes.
please do not use a dual plane intake, I took a performer off my 454 Camaro and installed the vic oval port and picked up 4/10s,,,, wow!!!.