[jeffspower]

I can't quite tell in your pics which rear end you have. Originally it could be a D44 or GM 12 bolt. It kinda looks GM? Most in the era with a GM rear had 3.07 or 3.73. Dana rear I can't recall seeing 3.07, but mostly 3.54 (not offered in the GM) and some 3.73. I don't think they used 3.42 until the early 80's in a 4x4.

Do you remember the tooth count? here's a list of the Dana 44 combos.

ratio RG/PG
2.87: 43/15
3.00: 45/15
3.07: 43/14
3.23: 42/13
3.31: 43/13
3.50: 42/12
3.54: 46/13
3.73: 41/11
3.92: 47/12
4.09: 45/11
4.27: 47/11
4.56: 39/8
4.78: 43/9
4.89: 44/9
5.13: 41/8
5.38: 43/8
5.89: 53/9