Here is some homework i've done for you although its an RM100X frame,its basically the same frame as the N,T 125s
With the RM100X cases in the frame.....its natural home
Now with the PE175C engine,similar engine design to your 125N but the cases are wider by approx 5mm
so your frame case mounts need to be widened.
Same 175C engine in the frame
Now we move onto the later PE175Z-E floater motors which is again 5mm wider to your 125N motor
Same 175Z-E motor in frame BUT is also wider at the sprocket side (further out) by about 8mm to the other engines.
These also had an extra case mount hole at the bottom.
I'm not 100% sure if the PE175T-X engines were the same design as the Floater engines (Leith and Luke would know)
even though i owned an X for 9 years,but i'm leaning towards a yes.
To add to that as well was that these engines had a bracket that is held/mounted between the swingarm
As the others also said,cylinder/reed spacings are all different as well.
All said and done,it will still be that engine mount brackets and chain alignment plus the fiddly time consuming
pipe,muffler stuff to do.
