Hey, Kens 50 PU, I was thinking the same thing!
I show a 15" option for '37 in the standard catalog, I do know that the '55 2nd came standard with 4 ply 6.70x15 tires, and that 15" 6 lug wheels were used on all 1/2 tons to '70, 4x4 1/2 tons to '87/'91 on Blazer/Suburban.