And about the switch to tubeless, I am getting conflicting reports -- one source, who has access to a vast library of old truck literature, is telling me GM went tubeless in '55, with tubed tires being optional (and preferred).
I hate to get picky to, but when you say GM, do you mean GMC or Chevrolet? Big differences in wheels between the two, or as Ive found out when I got my GMC COE...