the wheel axle input flanges on each diff do pop out easily and are the same diameter and spline pattern. They do insert into each other's diffs. But they are so different, you cannot swap 7-series input flanges into the M5 diff so you can then use 7-series axles. I'll have to figure out how much of the M5 axle I can use on the 7-series.
7 on the left, M5 on the right.