Commando Frames

They are not, 72 frames have slightly different headstock angle and special yokes that only go with that year, so not interchangeable. 72 bikes are notorious for weaving at speed, I know I have one, tyre combinations can make it better/worse, below national speed limit you won't notice. If you want to go fast only real cure is rebuild with later frame and later yokes.look on Norvil website under tech talk/ my bike weaves. Wonder why you are asking? Hope above helps

Regards Martin

The post Atlas style yoked 750 Commando's all have yokes with parallel stanchions to the stem and the same headstock angle. The 850's had a 1 degree change to the headstock angle and new yokes where the stanchions are at an angle to the stem. These angled yokes have ANG cast into the underside and have to be used as a pair, you cannot mix an ANG yoke with a non ANG yoke in a pair. This was to reduce the high speed weave, so to get the rid of the high speed weave you need an 850 frame and the ANG yokes. Andover Norton now supply the ANG marked yokes for both 750 and 850's.

71 to 72 changes to the frame are mainly to the side stand, the piddly circlip retaining the side stand is deleted and a new method of mounting. So using a 72 frame to replace a 71 would need a new side stand and mounting bolt etc so ending up with a more secure side stand. A 71 replacing a 72 can be done using a weld on plate from Andover Norton to keep the 72 side stand. 

Suggest you ride both, they are different to ride. Some like the 750 steering and some the 850.