I notice that Tracy uses rubber doughnuts between the flywheel and the
gearbox coupling, just for that reason I would assume.

As I understand it, there are two ways to avoid the resonance issue. One is
to make the drive coupling tighter, and the other is to make it looser.
Powersports chose tighter I believe, and the precision they need could be
why their drive costs $6000. Tracy chose the looser path. Both work fine.
The biggest unknown I face with the single rotor is the resonance frequency,
and how it works with the rubber dampeners that Tracy chose for the two
rotor engine. I may very well have to change the durometer of the rubber
dampeners, but I won't know until I try it.

Cheers,
Rusty