True. The 50 frame would almost be the same as the 51 except for a few holes needed to mount the 51 support brackets (see attachment). I don't know if the 50 slide/track and the fixed "C" bracket on the second cross member would need to be removed. If someone tries this, please take pictures.
One of the illustrations (below) from the Master Parts Catalog (MPC) is posted by Harold (above) - the 1951-1955st 1/2 ton spare tire carrier. Presumable, Chevrolet and GMC used the same style wheel carriers in that years.
Below, are both "generations" (3 styles) of wheel carriers (1954 Chevrolet Truck MPC):
left image = 1947-1950 (two styles) right image = 1951-1955st (one style)
Those images might help a little in showing/identifying the different mounting bolt locations?
I believe the side mount on the fender may have started in 1953. I had one on my 53 and frankly I hated it. Extra weight on the driver side, in the way when you exit the vehicle and just too bulky looking. I also think they were only on the driver side. Fords have them on the passenger side. I took mine off and put the tire in the bed. I am sure many owners love the side mount but not me.
Last edited by Sedgewick; Fri May 22 2020 11:32 PM. Reason: added text