In 1954, the 1-ton Platform & 1-ton Stake (3808 & 3809) had
a factory option for dual rear wheels, RPO-295. This factory option provided 7.0-18" wheels and 8 ply rating tires (and a mandatory RPO for beefed up springs and auxiliary springs).
20" dual wheels on these models would have to have been a Silver Book conversion by another company, an aftermarket change, or a special order.
As wbrowne stated above, 17" wheels were stock/standard on 1954 3800 trucks.
From 47-55, 15" wheels/tires were an RPO for 1/2-ton Chevrolet trucks (not just the 47-55 1/2-ton GMC trucks).
Tim
