My 68 Firebird resto is coming along nicely and I am going to build an engine for her this winter, and I am wondering if anyone has an idea what would be a realistic max torque/HP would be before twisting the poor old frame...and no I won't be using drag slicks, just street tires, so maybe I just answered my own question...I'll just buy more tires... I think the max HP was 335 in 1968, according to the books. My plan is to build a 455, not crazy HP but maybe 400HP, 500 ft/lbs ...is that reasonable in a convertible?