I found that the OS .91FX is "extremely vibrator" for some people. As I don't have any experience with .61+ sized engines, I'll try to minimize the vibrations, in case the rumors are true.
I bought three different engine mounts, and I don't really like any of them (Dave Brown, Dubro and Great Planes adjustable). I will use the adjustable one, as it let me mount the engine closer to it's base. I want to do this in order to keep the beams as short as possible, altough a supplement is needed (~12mm).