[fbarrett]

If you are talking about the left-side door mirror, the car came with one originally. Open the driver's-side door, and you'll see two rubber plugs where the mirror mounting nuts/bolts are accessed. Two studs (on the mirror) fit through holes in the door skin, and 10-mm nuts hold it in place. New "Durant" mirrors (with seal and inscription) are available from Stoddard Imported Cars.

If you're thinking about a right-side door mirror, you should probably forget it. I don't know if they were optional, but I tried putting one on my car ('65 912), and it was a waste of time and effort. You can't see diddly-squat out of it.

Ideally, the interior rear view mirror is used to see traffic behind you, and the left-side mirror is used to see traffic beside you. Aim the left door mirror out far enough to see cars alongside you. Most people aim the outside rear view mirror too far to the rear, not enough to the side.

Frank