I put a '78 750k rear rim on my '74 750k, with no problems, your '72 should have a 18" rim stock, and the '78 is a 17" stock rim, you may have to change the sprocket depending on which chain you plan to use. Make sure you use the drum from the '78, ' I can't remember if I used the axle spacer from the '78 or the'74. I'm very happy with the 17" rim and it was a easy swap.