DADS50 posted good advice. A few links he referred to are given below.

Contacting mothertrucker (MT) is a good idea. He sells those visors and I recall that he has extensive (the best I have seen) knowledge regarding differences in make and in versions for different models/makes/years. He might not want to be bothered, but it is worth a try.

http://www.jalopyjournal.com/forum/threads/repo-fulton-visor-sucks.469470/

Here is info (again from MT, I think) on 54/55 GM visors (especially the Chevrolet truck vs GMC differences in 54/55)

http://talk.classicparts.com/showthread.php?t=12083