Were all factory spare tire side mounts on 1947-1953 1/2 ton pick ups installed on the driver's side? Is a side mount with notched fender on a 1951 1/2 ton pick up on the passenger's side a home made or after market side mount?
A old Chevy truck history book says that the 53 had the spare tire mount as an option. It is on the driver side and required the fender indentation. Those boys in the 50's were pretty clever with body work. I imagine you have a customized fender, probably made with some roller tools much like the way they make gas tanks for motorcycles . That is my guess. Should be to hard to press it out using body tools or find a motorcycle custom shop and see what he recommends
If you have a decent right side indented fender I would save it and opt for a steel repop. I your fender is as nice as the one Allen posted to in his link, you could easily sell the indented one for as much as a reproduction fender would cost you. The left side 1/2 ton indented fenders are quite rare, I would say a right side would be a rare as hens teeth.
I have a tire mount on the passenger side of my 1951 long bed. But it’s obvious it was welded to the two bed stakes after market. This was my dad’s and always had a spare on it. I don’t have one now but plan to put one on with a cover.