How did you shorten the axle shoulder ? I'm lookimg at doing the same upgrade. I haven't boight motor yet because I've read that motor is 175 mm and rad runner drop out is 167mm.When I did this same upgrade to the bafang 750 on a single speed rad the new motor’s axle would not even fit back into the frame! Seems you did not have this problem? Where did you buy you motor and what is the O.L.D spacing? I had to modify the axle shoulder to fit. I did have the same problem with the chain alignment but that was corrected by carefully bending the chain tensioner/derailleur bracket. Really like the added power and speed of the motor, controller and display upgrade. There are a few gotchas but that’s what we get when we modify engineered equipment.