If your truck has its OEM wheels they are safe to use today assuming they are in good condition, you have them handled by professionals, aired in a cage, etc. What we never know, though, when this question comes up is whether at some point in a truck's life it might have had replacement wheels installed.
I've got a pretty good library of old wheel catalogs and other wheel literature. Three period references say that 1936 ton and one half Chevy trucks could have been equipped with either 20" x 5" or 20" x 6" Budd type wheels having 10 lugs x 7.25" bolt circle, and a 4.75" center hole. All the wheels cited used a Firestone "RH" rim/ring design combination. This is a solid one piece ring design where the ring has two indented areas on opposite sides of its inner lip. These allow the ring to be slipped (forced) past the rim during tire service. Here is a cross section drawing of that design.
http://i286.photobucket.com/albums/ll89/truckdog62563/Wheel%20Profiles/Budd1944FirestoneRH.jpgIf the truck had wheels replaced during its life, there were dozens of other locking ring designs used. It is very important that the rim/ring combinations be kept together as sets. It is very dangerous to mix match rim and ring designs.
The most dangerous wheel design, and one that no reputable shop will touch today, is called a Firestone "RH-5°". There is no chance that the truck came new with these wheels since the design wasn't introduced until the mid to late 1940s. But replacements could have been mounted. The following is a cross section of this design, and a picture of one showing the joint at the middle of the rim.
http://i286.photobucket.com/albums/...0Profiles/Budd1949FirestoneRH5degree.jpghttp://i286.photobucket.com/albums/ll89/truckdog62563/wheels/FirestoneRH-5degree004.jpgFinding shops to service these old wheels can be a challenge. Best to avoid places like Walmart or other general service shops. Seek out the big rig shops or farm equipment shops. Stu
Edit - I should add that the 5" and 6" width measurements were based on an old system of determining wheel width. The true widths were 3.75" and 4.33" respectively. Stu
