Re: Puch powered bike
You could try getting hold of the sachs motor that they did in the 60's. It was a 2 speed manual transmission - I think a 50cc but not sure.
"....Look, no pedals... *thud*..." The mating call of the motorized-biker.
"RetroEagle" - 32cc Two-Stroke, Piped. 35mph on #13 gear. Reversed stem with springer fork.