The article on the 477hp 318 states the heads were ex-SS heads.
If they were competitive SS heads, I could build a whole 500hp 408 for what those heads would cost.
You take the top end and cam off a 500hp 408, and put them on a 318 of the same CR....... you’re not going to end up with 500hp.
The 500hp 408 can be built by ordering pretty much the entire motor from the Summit catalog.
Deck/bore/hone the block, prep some heads, blend the bowls, an off the shelf cam from some catalog, bolt it together.....10.5:1, pump gas.......500hp.