Along those lines...
Back in the days both the OH-6 (Hughes 500C) and the OH-58A(B206B) came out with C-18 engines. The C20 was so much better that changes were made and lots of C-18s hit the surplus market. Nobody wanted them. I dont know if thats still the case, but Im guessing one could get one rather cheap if it was not to go into anything flyable. TBO does not apply to bikes. ha ha
So if your building a scooter with one, I would look for the C18 first. You wont know the difference when you hit the throttle on your scooter.........