1970 Duster remote mirror

I doubt that happens! it was not under back seat when I got the car! and I am pretty sure they do not remake them!
Point being, your build sheet could be decoded to tell what mirrors it came from. Build sheets are often under the rear seat springs but also can be found taped to the back of the glove box, under the bucket seat back covers, especially the passenger side, under the carpet and taped to the inside of the roof skin. Because your drivers door doesn't have a hole for the adjuster, either a manual mirror was installed or no mirror which I doubt.