I too had thought some or all 1954 and 55 Advance Design trucks would have the 5.25" center bore but I seem to recall seeing some with the smaller hub.
Am I misremembering or could some 54 models have the small hub still?

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-