Re: Hello. Please read
You can get 20-30 mph out of that type of engine, which is plenty fast enough for a bicycle frame/wheels.
The type of mount set up you are talkig about lets you release the roller from the wheel so you can pedal just like a "regular bike" search for "rack mount" and have a look at the Titan, Staton and others like it for ideas. Some have a drive roller (simple to make) some have a clutch and chain. Better in my opinion if you aren't going to pedal much.