There is a salvage '53 for sale on Ebay that in my opinion has a very unusual bed on it. There is no bed roll sides as is typical, but a 90º bend instead. Since the vehicle may be GMC rather than Chevrolet, is this standard?
Ebay Item #4603389434
I suspect the bed is non factory because it looks deeper than standard and the tailgate is different. Perhaps military?
Good job whether mfg. made or homemade.