Are you building this for YOU? Ambitious for a 70 year old
You know the farther you move the engine back the easier the lighter the front get's!!!! Honda really did a remarkable job cramming their engine in such a tight space, it makes it a real challenge to put a larger engine in. So are you going to put a sprocket on the old gearbox going to the jackshaft now? or mount a sprocket on the axle?
Not to steer away from this project- but what type of scooter is that?