How do you tell the difference between  a 3.89 and 4.22 differential?

From the outside, turn the diff input flange with someone counting
axles revs.
Block one of the rear wheels "This turns the unblocked axle at double
speed".

turn the input flange 5 times.

if the axles turn 2.57 revs, it be a 3.89.
if the axles turn 2.37 revs, it be a 4.22

From the inside "looking at the crown gear" there is
a stamped number on the outside of the crown wheel.

The number stamped on the 3.70 is 37X10 (37/10=3.7)
37 crown teeth, 10 pinion teeth.

The number stamped on the 3.89 is 35X9 (35/9=3.889)
35 crown teeth, 9 pinion teeth.

The number stamped on the 4.22 is 38X9 (38/9=4.222)
38 crown teeth, 9 pinion teeth.

The number stamped on the 4.55 is 41X9 (41/9=4.555)
41 crown teeth, 9 pinion teeth.

The carriers, are never marked, and the 3.70, 3.89 and 4.22 gears
could be in the Alpine carrier, and you would never know it.
This diff unit has the input flange low towards the ground.

The 4.55 carrier looks different than the true alpine carrier, but
fits the alpine case, provided the proper axles were used.
This diff unit has the input flange set higher at about the axle line.