Definitely not a 52 GMC bed. It would have had a wood floor, not a steel floor, and a cross-sill with a couple of extensions toward the front for bed mounting bolts.

I'm not sure when GM went to steel floors in the beds, but someone will be along to let you know.
A couple more pics would help ID what bed you have.

Kevin
1951 Chevy 3100 work truck
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1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car)
Busting rust since the mid-60's
If you're smart enough to take it apart, you darn well better be smart enough to put it back together.