While most cut down the flywheel, it is not really necesssary. Just saves a few ounces. I have used a conventional starter (sullivan) connected to a garden tractor batter (needs the extra amps),but I now have a diy starter made from a lawn tractor starter motor. It starts my 45cc homey effortlessly. Do a search for "JAG engines" for excellent parts. One thing about these conversions is you must respect them. With the large props and power they can do a lot of damage if your not careful.
Good luck, red