I recently purchased a rear wheel with a mounted tire from a '79 R65 on ebay as a spare for my '84. The tire on my mounted wheel was pretty worn out and the new (old) replacement seemed like the perfect solution. Put the replacement on, then get a new tire for the original and keep that for next time.
I pulled off the old wheel, slid the new wheel in and mounted it on the splines, slid in the axle, and went to tighten it up. To my dismay the shoulder on the axle pulled well into the wheel hub and the end almost pulled through the frame. I took everything apart again and examined the 2 wheels side by side. Everything looked identical until I noticed that the original wheel had bearing sleeves that were flush with the casting on both sides. The new wheel did not. I put my fingers in each side and could feel sleeves internal to the hub, but not visible.
So, can anyone tell me if the '79 model had a different axle than later years? The bearing sleeves on the original wheels do not appear to come out, so I am doubting that the '79 wheel had them and lost them.