Kx 80 to 125 motor swap?

I have a 1987 KX80 i want to no if a 87' kx 125 will fit or any 125 for that matter. and i no any thing will fit with welding and cutting and fabricating but i would appreciate some specifics if at all possible. the less work the better but i can weld and all that. didnt no if this has been done. any help is much apreciated.