Originally Posted by Howardwade
I tried a 11/4 and its to big.

Don't know what to say. Below is from 1939-53 GMC Master Parts Book. 1955.2-1960 MPB reads the same. I don't have a 1954-1955.1 book, but I doubt GMC would have changed it for a year and then changed it back.
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'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.