Vern may be able to add to this too. Here is what I have learned. There are at least two styles, and maybe a third style arm. The early 31 arm with a square end and the later style with a rounded end. The one original arm on my Mar/Apr 31 Victoria had a rounded end arm. Examples of these are pictured in my ad, neither have additional holes. The set I recently purchased have an additional hole that looks factory made, it is just forward of the two holes for the cross brace. So far I have not located a comprehensive report on the many different styles found on the Model A (17+?). One article in the Victoria newsletter lists 3 different measurements for different body styles but does not reference the stanchion height (4 3/4"). Also what is somewhat confusing is the difference between the picture, the drawing and what I think are original arms with two holes and the others with additional holes that could be factory or dealer/owner installed?