My 425 made 565hp on 92 octane on a "stingy" dyno, so maybe around 600 on a different dyno? W5 heads on an R3 block tho. It will be street driven and raced on pump gas.

Wouldn't be hard to make 600hp with Edelbrocks and some boost. My old 360 made 592rwhp on 18lbs of boost, pump gas with an a/w intercooler and meth injection, mildly ported R/T heads and a small cam.