The numbers cast into the shock arms are for identification by the company that cast the arm. IMO don't get hung up on MOST of the numbers. Pictured below are two 1940 shocks one red primer and the other black paint, both shocks have Ford script cast into the arm and the arms are 7 1/8" long C/L. The red shock has the number 10 in raised casting, F-837 on the outside of the arm. The black shock has the number 10 stamped into the metal, it is marked F-102-11-14 Logo 2 EEE on the inside of the arm. The Logo is a circle with capitol L inside (this is an outside supplier to ford maybe to Houdaille). Notice there is a minor difference in the casting of the arms but both have the same offset to their profile. Ford usually poured a bit of their own castings but usually used a couple of other suppliers to supplement. You can see the casting Logos on the intake manifolds as well as distributor body's. There may be additional 40 arms with different numbers in the casting but Ford wanted the number 10, the arm length and the slight offset to the profile will always be be the same. You can see minor difference in cast tools, intake manifolds, distributor body's.
