GMC 1/2 tons were standard H-033 (same as Chevy) 3.90:1 rear axles in 1955-56.
In 1956 an option for Spicer 45 rear axle was available in 3.07:1 and 3.92:1 ratios.
In 1957 only Spicer 45 axles were used and it stayed that way until at least 1959.
In 1960 (the last documentation I have) 1/2 ton GMCs used Spicer 44 rear axles. Available ratios stayed the same.
"Powr-Lok" was available as an option with either ratio in 1958-60.
Spicer 45 and Dana 44 rear axles share many, but not all internal parts. I'm pretty sure that the Dana 44 was just a renamed Spicer 44.
Spicer and Dana are actually made by the same company. The original founder (1904) Clarence Spicer was joined Charles Dana in 1914.
the "Axle code conversion" chat in the 1960 GMC Master Parts Book refers to an "axle code" of H-035 being a Spicer 44 axle.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12
'52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
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