Horsepower Guesses

That's a Comp XE262H, right? The regular RPM (not air gap) would probably be better (assuming that you mean you have the air gap when you say high-rise). With what you have, I'd guess around 280-300 HP tops. If it's an air gap intake, you might have a "flat" area under 1500 RPM, since it's not really a good match for the cam. Regular pump gas is all it should need, and using high octane probably won't do much for it. Really, with what you have, I think a Performer with a spacer would work best.