Regardless of what you may hear, big singles are going to be big shakers. The bigger they are, the more they shake. There is just no getting around it. While a big 100cc thumper may work fine in a lawn mower, where all that weight of the mower frame help make the vibration less felt, the same engine mounted on a comparitively featherweight model aircraft is going to shake the bejeezes out of it.

This is why starting at 70cc or so, single becomes rarer and rarer and twins starts to appear, and by 100cc, they are completely taken over by twins. Some over-square engines shake less, but I suspect most industrial engines aren't built to be revvers. They need to have good torque for the kinda of jobs they do, so they are more likely to be strokers.

Still, if you find a good big bore engine, by all means give it a shot. Still, I would favor one from a "handheld" device (eg. chainsaw, etc.) than from a "ground-based" tool (mower, generator, etc.). The engine is more likely to be designed with minimizing vibration in mind.

Good luck.