I remember some taillight/fender discussion a few months ago. If memory serves (that has been touch and go lately) the discussion was about raised tail light mounts on mid '60 fenders.

I tried some searches but came up empty.

Maybe you can determine the year by calling Mar-K (405) 721-7945.

Their catalog has dimensions, here are the 1964.
A stepside bed has fenders attached outside the metal bed sides and a step extending from the rear fender to the back of the cab.
Short Stepside: Length of bed wood 77 1/8". Inside width of bed 50”.
Long Stepside: Length of bed wood 97”. Inside width of bed 50”.

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.