Careful about buying a manifold for that engine, in the late 80's (86 or so)Chevrolet changed the mounting pattern so that the center two bolt holes on each side that hold the manifold on are at an angle as opposed to the other bolts, and then in the 90's they changed again to the vortec style of head. I don't know if they make a performer RPM (which would be my choice) for that style of head. You can modify the manifold to work by redrilling the center two holes on each side. Edelbrock does make a performer manifold that is made for that style of head, if that's what you have, although it's probably not much more than what you hve now. You would need to get a casting number off of your head to determine what you have. My boat started with a similar engine, 260HP but a couple years older, a cam with .480 lift didn't come anywhere near hitting the piston when I swapped out the stock one for a Comp Cams.