There was an optional high mount extended mirror that mounts on the upper door frame. The rear leg mounts in a hole much like you describe, with the front leg mounted further forward on the curve of the upper door frame.

My 45 has such a mirror, shown here:

http://s1048.photobucket.com/user/s...476_988333481_n.jpg.html?sort=3&o=16


1945 1.5-Ton Chevy Big Bolt
Maynard
In the Stovebolt Gallery
More pix of the old truck