Whipple has a kit designed for the carbureted HP500 engine as well as the EFI. It retain's your present carburetor and utilizes it in draw through fashion. The installation will add about 2 inches in height depending on your flame arrestor selection, I would recommend the larger 3.3 liter supercharger and intercooler. I would rate the engine at 700 HP @ 5250, and the parts all come blue to match the Mercury high performance colors. You should also add nosecones for additional water flow to feed the intercooler. The B&M 250 your considering will need an intercooler which makes it much taller and will probably make 600-620 HP when completed. Since your so connected, I'll offer you a special OSO discount price!!

The Whipple's and a set of five blade Herring's should get a twin step Top Gun to 92-93 mph.