Deacon man you got to break down and buy yourself a wire feed welder you could become famous for custom motorized bicycles it won't take you long to learn how to weld being retired you could get lots of practice and even help out your friends when they need something fixed. You have hidden talents that you need to tap into. You know what I mean?!
Norman.
If you can find an engine with bearing on both sides of the crank it will work better for what you want to do. A single bearing engine will have a huge force put on it single bearing when used like you are going to do. I might suggest a friction roller at least 1" in dia. and use a hinge to engage and disengage the engine with a lever in front of you. Just some BS for you to think about. good luck on your bike.
Norman