Re: 50cc GY6 on a Bicycle??
While that may be plausible L2 it would be quite a bit of work.
That still leaves the issue with gearing being based a 10/12" wheel. Not an issue if running a smaller wheel in the rear is acceptable. There are plenty of optional final gear sets but I doubt any low enough to accommodate a bike size wheel. Of course one could run a small front wheel to balance things. Might be a 21st century Cushman.
Austrich, the reduction I am referring to is the case on the engine. It looks like a 3:1, The 49cc really needs a 5:1 and the more expensive kits come with them. You can determine by removing the reduction(4bolts) and counting how many turns the clutch drum makes for one turn of the sprocket. I'm betting 3.