$$$$$ Chris (440pursuit) made well over 600 w/ an iron headed (indy I think) 431. You'll need the best heads you can find/afford, roller cam and as much compression as you can. I'd probably look at going boosted as the drivabilty is much better. If you go N/A you'll need 12.5:1 and that means race gas or at least a water/meth injecton kit. What is your goal?