I agree it sounds crazy. Things were not as anticipated back then. I've seen things like that. They only last a year or two until factory changes to common sense. Sometimes a component was attached to another prior to assembly in truck. They thought it was a good idea. Never realizing it was then "locked" for repair. Hope that is not the case. I don't know 1939 either. We all know that for many years maintenance/repair was not a design parameter. Bolt access was not considered. Not much better now. Pull the motor up to get oil pan off? No problem. Drain and pull the radiator to get fan off? No problem. Can't get the inside starter bolt off without taking tire and inner fender off? No problem. Oil spills all over because filter is mounted horizontally? No problem.
In 60-66 GMC, I have seen factory riveted cross members and factory bolted cross members. On the riveted cross member, motor was too long to remove with 4 sp. Could not get 4 sp out after unbolting from bell housing until rotated, rolled, jammed and slipped down. A 150 lb slug of iron waiting to crush your face and decapitate your fingers. Lots of fun. I would have rather gone to the dentist.