RE: An HPI truck .28 engine with 2.9hp or OS .32 marine engine with 1.1hp for 36' fiberglass hull?
2.9 horse power at what RPM? Is that another of those manufacturers ficticious horsepower claims at an unobtainable RPM? You would be better off with a good marine engine that is designed to operate with the prop loads it will see in a boat rather than a car engine that is designed for light loads and will be a dog in a boat.