I think that someone changed the wheels and tires, from 56 to 58 all Chevy and GMC trucks went to tubeless but they were not well received buy the skeptical consumers. Chevy and GMC were truly ahead of their time but old truckers and farmers can be rather hard headed and reluctant to change LOL. In 59 the tubeless tires were standard and the tube type became an option then in 60 tube type was again the standard and the tubeless became the option till the late 70s early 80s.
Good luck with your new truck it looks to be in much better shape than my 56 GMC and I have been asking $1000 for it so I think you did well.
Is that 11,000 pound GVW metric? My GMC is 14,000 and I have a heavy duty 71 Chevy 1 ton with a 12,000 pound GVW.
