You are correct on the parts description but they are plates not nuts and there are actually are at least three versions of them, I believe the reason you may not be seeing them is they are part of the cab assembly. By their design they are not considered a service part but assembly parts. Examples of types, early serrated versions 1947-51 and smooth versions from 52-53, 54-55 are slightly different.
http://www.flickr.com/photos/advance-design_parts_co/8129329170/in/set-72157631868452754
http://www.flickr.com/photos/advance-design_parts_co/8129329572/in/set-72157631868452754

1950 Chevrolet 3/4-Ton 3600
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