First, welcome.

Now there are a couple of guys here that are a minute away from releasing a jackshaft set up to run a frame mount through your bike's gears...see Pablo or Ghost0. I don't know if that hels, since they are made here.

Have you considered contacting Whizzer, or the factory in Taiwan for just the engine?

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If it ain't broke, and you mess with it long enough, it will be.