A small block in my boat = death. Even if I hacked the engine bay up enough to fit one, the weight would kill the balance of the boat, and my outdrive wouldn't take that kind of power. I've have to upgrade to the Bravo series....very expensive to do.
The only upgrade motor that would make any sense on my boat would be a 4.3L. The only problem is the cost of converting the 4.3L I have here would be more than just rebuilding my current motor.
4.3L exhaust manifolds alone would cost me about $600. Gotta do custom motor mount, most likely different bellhousing, flywheel, starter, alternator, convert boat to having an electric fuel pump or convert motor to a carb setup w/ mechanical pump, flame arrestor, exhaust riser, and some other stuff I probably don't know about. Boat-specific items are always more expensive than comparable automotive items too. The SBC kits (haven't seen a 4.3L kit) to convert an automotive engine for boating use sell for about $1800.