Ok, I don't have a Dana book, so I'm asking on here.
I have an 79 F350 4x4 with Dana 60 front and back. It has 3.54 gears on both.

Rear:

3.54 D8TA TB
603901-1

Front:

630093B on left side of the housing

3.54 D8TA YD
610023-2

Does those tell anything other than the axles being 60's and 3.54 gears, like if it has limited slip?

I am going to change the gear oil on both axles. What gear oil should I use? 80W-90? Or 80W-140?

Thanks!

 

If the Tag said 3L54 then it would be a locking rear.

So both front and rear are open diffs.

Ford never sold a locker for a front diff.

The Pro60

 

Sorry 80w-90 should work great!!!

The Pro80w90

 

Your front axle is a standard axle with 3.54 gears a
610023-4 would be the Trac-Loc Equiped axle which is the
factory limited slip your rear axle is also a standard a
603901-10 ,-11 ,-12 would be a Trac-Loc and a
603901-9 is a Detroit No Spin in the 3.54 for the rear