This engine is the same as a legal 70-71 440-6 bbl engine. You are just allowed more lift and a single 850 cfm carb. Lift on the 70 6 bbl engine is .455" Intake & .470" exhaust. The lift on the 71 6 bbl engine is .468" intake and .483" Exhaust. The crate engine is allowed .533" lift Intake & Exhaust. The 850 holley is a wash. I would think a well prepare 440 crate engine could make somewhere around 600hp. Jim