I have a Checkmate 253. The 27 ft fountain is a stepped hull and has a blue motor 454, rated at 450 HP. I've raced him about 10 times this summer. It's always close but I pull from him every time even when I had 4 passengers and he had one. 496 Bajas are no problem for me.
To give you an idea during the LOTO shootout three weeks ago the winner for my class NV1S1 (Non-professional, V-bottom, 22'-26' length, Stock power, 1 engine) ran 71.
I don't know if your headers would bump you into the modified stock power class but a cam definitely would.
Either way 76 is rolling on the water.
I'm still trying to decide if I'm going to switch to EFI setup over the winter and a labbed prop or just get my prop labbed and hope to pick up 3 mph.