lockers question
assuming the diff has no labels, etc, or MWO tags, and it is plane jane, can't you do the old-fashioned locker test by jacking up the axle and (with both wheels off the ground) rotate one wheel, and check for direction of movement of the opposite wheel?
Theoretically, if the wheels spin in the SAME direction, you have a posi/locker....if they spin in OPPOSITE directions, it should be an open diff without posi.....
Not that I have a 5-ton with Detroit Lockers, just going on the old 4x4 info I learned way back when (my first 4x4 was a 76 Scout II with Powerlock rear diff, 345 V8, with 727 Chrysler trans and Warn lock-outs....awesome truck)
Adam