Gary,
These are the two rifle brackets I salvaged from that scrap cab. Note they are not identical. Not even close as it turns out, and both are diffferent again from the two which are on my cab (Ford). I believe these were Chev, because the cab had a sunshine roof. The sunshine roof frame was the only bit I wanted, but couldn't see these thrown away.
The smaller one.
The larger one.
Note, both of these were welded to the cab rear panel, and had to be cut off. The spring steel parts that rifle clips into seem to be sound on both. Would be a big job in making brackets to suit.
Mine were bolted, but as I said, mine are Ford and I suspect these are from a Chev, cab 13.