I just cheat big time. I use a hole saw to cut the center out of the flywheel, dress it down on the o.d., drill it for a magnet, and tighten my prop adapter against that. Works great!

Sometimes I don't even use a prop adapter if the engine has a long crank snout, or if I have a "stud nut"...

(One of these engines turns 9000, the other 9400 rpms. No abnormal vibration, never have loosened up in many, many flights.)

AV8TOR