..the problem i see, potentially, would be that the 125 engine/gearbox...all one piece..looks longer than the 50...
..there are dual shocks on the 125..
..look at the service manuals of both scoots..
..there are links to them in the general board...
..check the "overall scoot length" spec for both..
..if the 125 is longer, then there might be a problem in a swap-out...