One thing that can help you down the road when you are modding your boat is the use of hydrofoils. The most resistance to movement that a boat gets is due to the amount of water that it has to push out of the way. By lifting your boat off the water, or simply having less boat in the water, you will improve your MPG or batt efficiency. Most hydrofoils act as a wing and, as you move forward, LIFT up your boat. There is also the pontoon approach which also can reduce water resistance.
Hydrofoil:
You are asking what equipment other than forklifts have good motor salvage chances. Are you looking for speed or power? (eg: light and fast, or heavy)