I was actually just making a prop hub for one of these exact engines a few days ago, starting back on it tonight, if you have a lathe or other means of cutting the center out of the flywheel and putting the magnet in that, then all you need is a standard ryobi prop hub to get it going, from what I'm making, the prop hub needs to be about 1 3/4" long to mount at the front of the flywheel and bolt on a Master Airscrew 18-8 or 18-6 prop, it's basically just a spacer... I was trying for having just enough threads to get the prop on with a prop washer and not have too many threads left