The fronts and the spare are all the 15" multi-piece single rims that you mention.
Based on the ID tag gross weight (6500), I'm pretty sure the duals are not original to the truck. The overload springs are also a completely bolt on arrangement.
'38 Chevy 1-1/2 ton '49 Chevy 1/2 ton '54 Chevy 6400 2 ton '55.2 GMC 3/4 ton '56 GMC 1-ton
