Ben,
Well, I don't really know if 500hp is managable - I don't have my Cobra on the road yet.
For a 351 stroker, about all you'd want to re-use from the stock motor is the block and timing cover. You'll need a stroker kit, which is crank, connecting rods, and pistons. You'll also need a new cam, aftermarket heads, intake, and carburetor.
I've got pictures of the parts I used in my 408W on my
website.
Pete