As far as the frames go, the craddle on the 125 is alot shorter and steeper Than the 250. However, unless it's a Gen 1 250, you will have to modify the frame to accept thr 500 motor. 125 frames require a bit more craddle mod than the 250.
there may be shit loads of info here but it never hurts to ask.
may be some one called put up a common ask question section or find a fact area on each GEN frame.
i meen when i first started i didnt even know what an AF was and the term poped up all the time.
"not speeding officer".....qualifying
CR250 97
CR500 AF 99 (in progress)
CR500 AF CR G-4
CR500 1985 true legend
RGV250 96 X2
GSXR600 07 TRACK BIKE
VH Commadore cup car (race)