383 knowledge anyone?

What Demon said. The 383 blocks cannot safely handle 600hp without some attention to details. With a roots blower or centrifical, I would lower that number to 550, and I wouldnt run a longer stroke than 3.75. There are kits to stick 4.25 crank with chevy sized rods in there I believe. But really, 500 hp is easy with bolt ons and good heads.