ORIGINAL: rcbif
ORIGINAL: Ozpulse
Probably the easiest to convert is the 30cc RYOBI/Homelite long shaft motor as you can put a spacer with backing for your prop, mount from rear crank cover bolts with some alloy angle!
x2. Wackerengines.com has all you need for it. Only downside is no original pullstart once converted. I use string wrapped around the flywheel.
You can install the pullstart plastic wheel over the spacer behind the prop, it still engages the arms on the flywheel and already has a slot in it for the knot in you starter rope.
Sort of a geezer wheel conversion!