Re: 125cc engine!!!!!!!!
look up the Kikker 5150 bobber with the Lifan horizontal 110cc engine. it's not a Schwinn, but it might give you some ideas.
i keep expecting to see one of the geniuses here figure out a way to use the 50 or 70cc Lifan horizontal on a bike, like maybe a board track style. Houghmade, are you listening?