The box is fairly rare, but that doesn't necessarily mean valuable. As for the bolt on extensions, I've never seen them or heard about them. I wonder if somebody did their own modification of a 3/4 ton to use a 1 ton 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.