Please see the link posted about the drive shaft interchange.
1988 740 GLE automatic

The car is on stands & with the gear selector in Neutral I can turn the shaft while holding on to one of the wheels with the other hand.
I'm not sure if it takes a certain amount of torque to "catch" so to speak.
It does still drive but with very little pulling power and some noise (this noise appeared one morning and i thought it was the center support bearing finally going out after two weeks of squealing)
Turns out the squealing bearings were the least of my problems. After placing a good drive shaft with good center bearings and all, the noise and lack of pulling power are still there.

Is there a True test that tells me the rear end is completely shot?

I want to make sure before i pull the rear end from my '90 745 turbo & place it in my good ol' 740 GLE.

Any comments appreciated.
--
"Many people fail in life, not for lack of ability or brains or even courage but simply because they have never organized their energies around a goal." Elbert Hubbard