You cannot tell what the delivered wheel size was, unless you have the original order/receipt form.
On Chevrolet trucks the 16" wheels/tires were standard and a 15" option was available. The 15" tire diameter was most likely a little larger diameter than the 16" tire diameter.
I do not know about 1/2 ton GMCs in 1954; but, I think the GMC wheels might have been multi-part/piece.
