With quite a bit of filing, sanding and buffing, the mirror stalk looks a lot better than it did when I unearthed it from the parts stash.
The original mirror part was degraded beyond repair, so I used a mirror from a[n]
7 Series E21, which got a little touch-up paint. You can see the size difference between the new and old.
The headliner will cover the black plastic receiver.
EDIT: As it turns out, this is an E21 mirror. I found my 7-Series mirror, which is substantially larger, then I immediately and clumsily dropped it, breaking the mirror.