Please check my math: Rear End Gearing

[Nuckingfuts]

So we're still getting a pulse on this truck's (73' shortbox) specs & general health and so this weekend we are going through a laundry list of checkpoints, one being to I.D. the rear end. The only markings I could find so far on the rear end are 3896839 and 'N' just below it, these markings were on the forward/passenger side of the pumpkin. After some research I came up with no clear answer and therefore tried the 'jack it and count it' method.

With both rear tires off the ground I could spin one tire forward and watch the other spin in reverse......but only for about one rev before the other tire stopped spinning. The opposing wheel spin makes me think it's an open diff but the fact that the opposing tire stops spinning in reverse after some initial rotation has me confused.

Let's set that aside, counting the wheel rev's to drive line rev's I came up with this:

Method 1:
Both tires off the ground and just turning one tire while the other was allowed to free turn (actually it only turned for a partial rev then no longer rotated during test).
8 wheel rev's : 12.25 rev's

Method 2:
Both tires off the ground but one wheel being held static while the other is rotated.
8 wheel rev's : 12.25 rev's

Both ratios appear to equal 3.08s....am I wrong here?

I'm not ready to open the rear end just yet to verify so I thought I would run it by you guys first. Is this open diff? Do I have a good estimate to assume 3.08 gearing? Thoughts?