Since my new petteroid is a hopper I looked for some balancing info. Wasnt as easy to find as I thought it would be so I thought Id share it here. I contacted some people who do balancing and at the RPM our motors operate they say this proceedure should make them smooth as silk. You must of coarse either attach, or separatly balance your flywheels.
http://modelenginenews.org/etw/etw_bal/p2.html
That's a pretty good description/explanation of how balancing will also unbalance a single cylinder engine. You can turn a hopper into a slider, or you can turn a slider into hopper, but you can't eliminate both at the same time. I don't know for sure which would live a longer life in a rigid mount...but I suspect the hopper would for the reasons briefly mentioned. The hopper is certainly preferable for a resilient mount since that is exactly the mode the resilient mount is designed to attenuate.