I own a 1958 GMC 250 with a GMC 270 L6, SM-420, and an Eaton H072. I also got a 1957 GMC parts panel with a dual rear wheel axle in my truck purchase, but it was heavily customized (extra frame jacks, tool boxes, and vents welded/cut into the body). Allegedly the 57 was used by some sort of oil drilling company in the Kansas area. Both trucks spent most of their time in the Midwest. Both trucks have inner wheel wells similar to a typical 'tub-kit' as seen on hot rods at a quarter mile drag-strip.
Both trucks were equipped with 19.5 inch 1-piece Kelsey Hayes wheels. They use flat bottomed castle-nut style lug nuts to retain the wheels on the axles/spindles. Between both trucks I was able to create 1 usable set of 6 wheels. Tire size is 8R19.5.
If you have the GMC maintenance manual that covers 55-59 trucks it has a section which details the types of wheels available on these trucks (2-piece, etc...). The Kelsey Hayes wheels are mentioned in there.
My personal experience of strutting around old fields full of these larger 'Big-Bolt' trucks is that the Chevrolet's typically had 5 lug and 6 lug wheels of different bolt patterns. I have not personally seen an 8 lug Chevrolet, but that doesn't mean that they didn't exist from the factory. When I have seen GMC trucks from this time period, they're at least 6 lug or 8 lug.
Below is a picture of my 1958 sitting at original ride height on 8R19.5 tires. The white truck next to it is a 2005ish Chevrolet 2500HD for comparison.
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