You sure those aren't 16" ????
Seems like most everything was 16" in the 1950s and then in the 1960s they went to 15" on the half ton six hole, and stayed mostly 16" on 3/4 ton (I know there were some "odd" larger wheels). I'm not a trivia expert but I've just owned or driven or worked on a lot of old trucks. I bought a nice pair of 6.50-16 mud/snow tires/wheels for my old 65 C10, but the wheels/tires that came with it were 7.00-15. Those work out to about the same overall diameter.