If im reading it correctly you want to put an old shape sr125 tank in a new shape sr50? in this case it will not fit the bikes are two completely different shapes meaning that the tanks will also be.
Russell, what grounds are you basing this on? I know theyre two different shapes, as stated old shape and new shape, I also I own both models, but didnt want to strip the rear ends to find out.
They look totally different but I'll take a closer look when I'm next at my garage. Got both a 50r and a 125.