Checked my CR 250 jigs today.
They are very close.
It seems the mounting brackets are the same distance apart but the front mount on the 80 model is about 8-10mm further inwards.
80 model is also about 5mm shorter in front of the front mount.
Think the angle is slightly different too but not by much.
I remember having to make a jig for the 80 model as the the 79 just missed out on fitting the 80 properly.
If your cool with mods in wouldn't take much to modify either muffler to fit the other model.
I think you would only need to change the steel stinger part in front of the muffler body.
I'm still a bit vague on the 125's of 79 & 80, I really need to get a bike in some time to check them out properly.