Dont think anyones mentioned this yet- But 600 whp is FAR different from 600 crank hp.
Arent there people on Hz making 3-400 whp with realtively affordable mods and bolt ons with stock blocks? Maybe the guy meant close to 600 crank. If you figure for a moderat 20% drivetrain loss youd only need in the 480 whp range to make 600 crank. Considering what people do with fairly stock blocks, is that too far-fetched of a number for someone with those manifolds, a stand alone, that turbo, that huge ass fmic, and forged goodies?
ALso from what ive seen when youre making numbers close to that, a little head work seems to go a LONG way, I believe chris' car is a perfect testimate to this. Should ask the guy if theres been any head work. With those mods hes listed i wouldnt be surprised to find at the very lease some porting and polishing. Hoepfully he didnt mention it already and ive just missed it.. hah.