If you want 500hp, I wouldn't bother with anything other than a '70 factory block, Scat crank and rods, and a nice light piston like a JE. Capacity somewhere around 377 to 408 cubes, using 3.7" to 4.0" stroke.
There are lots of guys making 500hp with 351W blocks. Cranky knows a lot more about the Dart block, but my SVO block needed heaps of machining as delivered (cylinder bores, tunnel bore, lifter bores even need honing, decking, etc) Lots of money to throw away if you're just planning on having a nice street motor.
If you're putting gumballs on the side, and a helmet on your head, well then I can see you wanting the strongest parts available.
So, how about a Sprint Car WoO 410 motor. Drop the compression a few notches. Convert the Kinsler to EFI, replace the maggie with an MSD. Now we're talking!!!
