From the 1954 GMC shop manual (I'll assume your
copy is on order):
Model 101-22 has single a torque tube
Model 102-22 has split enclosed shafts connected via U-joint, rear shaft is identical to 101-22
Series 150-22 Front shaft is solid, rear is tubular. U-joint trunnions have needle bearing support rings.
Series PM150-22 AND UP Both shafts are tubular with the needle bearing trunnions.
When two shafts are used, there will be an extra crossmember with a center bearing supporting the front shaft.
I don't know what changes were made between the 54 and 55.1 versions of GMC trucks, but a lack of torque tube on a half ton may be the best evidence of a later model. You will find much arcane GMC knowledge at www.oldgmctrucks.com