i am thinking about buying a project boat with a locked up merc 350 no big deal to me but if i do which parts other than carb, distrib, waterpump need to be marine parts on a new engine if i were to build one?
Exhaust manifolds, thermostadt housing. And if you don't plan on using a Marine engine dipstick tube, you will want to replace the oilpan drain plug with one that has the drain hose that can be run out the bilge drain. Seems obvious, but you will hate yourself if you think of it after the engine is installed.
