for testing purposes, I use a V-belt pulley with the appropriate Taper-Lock adaptor. In your case (3/4" shaft), probably a 1210 or 1610 Taper-Lock and a single-groove pulley where the bottom of the groove is larger than your prop bolt PDC. Single chain sprockets can also work. Then mark the PDC and drill&tap the holes.I bought one of these Tillotson 212cc engines last December. I've got it mounted to an engine test stand for experimentation. I recently bought an Xoar 36x12 propeller to test with it. It should take 9 HP at 4050 RPM and 10 HP at 4200 RPM, but I need to figure out how I'm going to mount the propeller before I can proceed with any testing to verify any of this.
My first attempt was to draw up in CAD a custom propeller interface to mount to the shaft. However, having the parts made as I drew them is going to cost a bit more than the engine, so I'm looking at different designs now and other alternatives. If anyone has good advice on how to inexpensively add a propeller interface to a 3/4" straight keyed engine shaft, I'd sure like to know about it.
I figure there is about a 50/50 chance this engine investigation is a wild goose chase, but maybe it will bare fruit in the long run. Couped with the right design, it has the potential to be part of a very affordable ultralight.