Is it an inboard? is it in the boat now?
Make sure you use the right paint (high heat tolerable) all of the extirior surfaces, even hoses and oil/fuel filters can technically be painted. Make sure you cover any intake/exchaust: you do not want the paint (or vapors if cans) getting inside. If you are painting hoses, etc, make sure you have a record of any part numbers you may forever hide under the paint.
One last note, I would not recommend you paint your alternator, or voltage regulator.