All this talk about the McCullochs has me wanting to get mine converted so I can see how it does and if it has vibration, etc. I'm not sure why it would vibrate unless it has bad bearings or something. One trick you might try, is to install an un-balanced propellor. Try it with the heavy blade in line with the crank counterweight first, then opposite. When the piston is all the way up, the crank counterweight is all the way down, so install the unbalanced prop with the heavy blade down. If that doesn't help, reverse it and try again.

Ralph, did yours vibrate noticeably more than normal??

Good luck, and keep us posted please,
AV8TOR