Jeff my build date is 4 18 66 ; what do these numbers indicate? ?? April (4) 04? ? 3rd shift??
So it looks like you have the same 4043 on the drivers side twice.
Considering that location is not a typical location for any writing of this kind and that it matches the fender number I think it would be a wild coincidence
Not sure why he applied the number above then below as he didn't didn't do the same thing on other cars. Maybe he just saved some effort and wrote it once from then on when no one corrected him
Here is another example of "Fill-in Fred" or at least the fender number being applied in the same non-typical location on a later 66 San Jose car than yours
Been studying marks and such since the 80's and have over 8,000 examples currently and adding all the time so do have others
BTW where did you get the April 14th date from as a build date?