[FirstOwner69]

Those look like the same style as the stainless mirrors I saw on a '79 van that I got a tilt column and a mirror head from. The only visual difference is that those on the van I looked at had bolts rather than studs with acorn nuts. I found a lot of similar elbows with varying leg lengths on vans as well as some Ford trucks into the 90s, but they all had female threads rather than studs. The shiny ones were of stainless vs. the chrome originals that rust. I made studs from bolts and bought some chrome acorn nuts which were the only ones I could find with the correct shape. The van mirrors also had elbows with the shorter horizontal leg like yours which is kind of nice since it tucks the head in a little closer to the door without reducing the field of view a whole lot on the passenger side.

Here is a picture showing the '72 truck mirror base dimensions.