Ok, got me puzzled here. Many GMC 1/2 tons of that vintage had a Spicer 45 rear end. The Spicer 45 is very similar to a dana 44. It would Not have a dropout 3rd member. Some GMC's got the chevy rear end, which was made by Eaton. This rear end would have a very round cover bolted to the back and a dropout 3rd member in the front. Both these axles would have a 6 lug wheel pattern.
Possible ratios for the Spicer rear are 3.08 or 3.92.
Possible ratios for the Eaton rear are 3.38 (after market), 3.90, and 4.11
