It can physically be done, but is probably not economical. What is your precise model? If you have an M18C2, many parts are no longer available, so keep that in mind. Doing any work on these may be a waste of money. Great motors in their day, but that day is past. Those motors came in 4 different lengths: S, L, XL, and LL. The "spacer" extension housing determined whether it was XL or LL, so removing the XL extension housing would get you back to L... But... to convert length... in addition to the spacer, you need the correct driveshaft, water tube, and shifter cam rod. If you can find the parts to do the conversion, they will cost much more than the motor is worth.
