Plenty.
1. Does the new engine have a charging system and flywheel with ring gear?
2. Do you have room to solidly mount a battery?
3. Where are you going to mount a solenoid, a switch to start the engine, a switch to shut off the engine?
4. Do you understand electricity enough to hook up the charging system to the battery, solenoid and the switches?
5. How much do you want to spend? It can get pricey.