Look very closely at the backing plate for evidence of spot weld marks where the L-shaped sheet metal pieces used to be located. This is where the spring retainer hooks attach to the backing plates on some of the Huck brakes. I have also seen Huck backing plates with no evidence of ever having these angled pieces. I have also seen them with holes drilled for the more modern spring retainers. I don't know if some of them didn't come with those springs. The way that the Huck shoes are mounted at the bottom (pivot pins), these springs don't seem to do much when compared to the more free floating mounting of the shoes on Bendix brakes. Bottom line, I don't know the answer to your question and I haven't found a manual that describes all of the different styles of retainer hooks and springs or if they were not used in some cases.
