I don't have Chevy literature for that year, but do have a Motor Wheel Corporation listing from 1942 that covers you. It shows for 1932 through 1935 the wheels were 10 lug x 7.25" bolt circle with a 4.25" center bore. Available sizes were: 20" x 5" rim with 7.5" of dual spacing that allowed a maximum of either a 6.50" balloon tire or a 6" high pressure tire with 8 ply rating; a 20" x 6" rim with 9" of dual spacing that allowed a maximum of either a 7.50" balloon tire or a 6" high pressure tire with 10 ply rating; a 20" x 7" rim that used a spacer to achieve 10" of dual spacing and allowed a maximum of either an 8.25" balloon tire or an 8" high pressure tire. It also shows a 20" x 7" single rim with 2 3/8" dish that allowed either a 9.00" balloon tire or a 7" high pressure tire. The 5" and 6" rims were Firestone's "RH" style lock ring design and both of the 7" rims had Firestone's "R" lock ring design. What the difference was between balloon and high pressure I can't say. That's maybe a question for Coker or Jim Carter's folks to tackle. This info is for a Chevy but if your truck is a GMT it all changes and gets more complicated. If that's what you've got I'll have to post the chart I guess. Stu