500-525 hp 468?
See my post in this thread. Build your own 454 based ported big valve oval port head motor.
All you need as a base is a usable Mark IV 454 block and OEM cast crank, 049 or 781 heads and a good local machine shop.
You can do the head porting yourself. The machine shop does the machine work.
If you cannot swing the sweet street roller cam and kit (comp # K11-771-8 or K11-772-8 use a similar duration @.050" solid fat tappet street cam. EG Comp 11-551-5 or 11-678-5.
These cool and powerfull street roller cam kits are worth spending a few more pennies for.
if you don't want to use the RPM dual quad manifold and carbs use a Performer RPM and 800-850cfm carb.