I'd guess about 56 or so for a few years after that.
although I'm pretty sure tubeless wheels on a 1 ton were usually 19.5" early on.
I've seen 17.5" Chevy wheels with fewer lugs as often used on NAPCO 1/2 tons.
Can't say that I've seen 17.5" on a 1 ton Chevy, but would not surprise me in the least.

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
---All pictures---
"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-