7.25 drum to drum measurement
I just measured the thickness of a new drum.
0.136" thick each.
If you measured axle flange to axle flange add 0.272" (0.136 + 0.136) to your measurement.
I measured my loose 67 7 1/4 and came up with 57 outside of axle flange to outside of axle flange.
There was a slight deflection over the center of the diff.
That would make it all in 57.272"
The posts say 57 1/8"
Which is a little under an 1/8" less than I measured.
I bet if you measured 100 rears you would get 100 different measurements.