Don't forget the bottom end of a "standard" 350 isn't the same a marine engine. Boat engines turn alot more RPM for an extended period of time vs a car engine, just to let you know in case you didn't know??
Years ago we bought a 21' Sunbird with a bad 305 in it, and put in a mild built 350 and propped it and picked up around 9 MPH, and then bought a Rinker 23' with a bad 454, I had built a 496 for it with some serious HP(around 550) and re propped it, the Damn thing was wickedly fast, stock was suppose to be around 50 MPH, after the getting it done it went 68 MPH on a radar gun. I miss boating... That was a total sleeper!