If you plan on using the electric PTO (if equipped) and lights, make sure you buy an engine with an alternator. I have thought about attempting a Harbor Freight or the like engine swap, but then realized that few, if any, have a charging system capable of doing more than keeping the battery charged. Keep this in mind when searching for an engine. Also if you want to keep the original fuel tank, you will need to add an electric fuel pump. I have thought about using the under-the-seat tank as primary and the one mounted on the engine as a reserve, but can't find an engine I like with an alternator. I am very interested to see how yours comes out.
Ryan