I was thinking about using bearings from an alternator for a car. You would have to get a shaft to fit those bearings. The bearings are permanently sealed, so lubrication wouldn't be an issue. As for the shaft; I don't know if you could use aircraft 6061 aluminum or not. Would if be strong enough or would you need a steel shaft?

You could weld a few brackets to the bearing housings or make a sandwich bracket to hold the brearings and then weld to that.

I figured a 1.3:1 ratio. With the engine at 10,000RPM, then the prop would be turning about 7700RPM. Or at 1.4:1 with 10,000RPM the prop would be turning about 7100RPM.