My 53 came with the side mount spare tire carrier and it was bolted on to the bed and looked like it was as original. It was fastened just as you described, hex head bolts and washers. Most were so rusted they broke off even after soaking with Kroil, but I got one or two to use to match up when we reassemble.
Mike

My old truck's still running good, my ticker's ticking like they say it should, I got supper in the oven, a good woman's loving, and even my bad days aint that bad...Yeah, I'm a lucky man!
1953 Chevy 3100 Shortbed

1965 C-30 Panel Truck
1963 C-20 Long/Fleet Pick-up California Black Plate