I don't know for sure but I think 1951 to 1954 is not a good comparison. 1954 was a major change in the beds. I would offer up some measurements from my bed but I have a one-ton long bed and don't think it would be helpful. Are you sure you have a 1951 bed?

1953 Chevrolet 3600
Fried Green T'mater (Vern)
In the Stovebolt Gallery
Caution: Political Statement
Man who runs in front of car gets tired, man who runs behind car gets exhausted.