I think that there were two different types of rear bumpers. My 53 half ton panel had a heavy, thick rear bumper. It was quite different from the front. Maybe a PO put a bumper on from a big bolt? I acquired a front bumper off a pickup to replace it with. Weeds, I think you could likely repair the hole without weakening the bumper, it will still be better than the bumpers they make now-a-days.