I added one to my '70 Challenger. It was an option on that year. Glad I did. Helpful on the street and on the track.

I used the Y1 re-pop of the factory mirror. Painted it up to match the body and installed it. I measured 3 times instead of the usual 2 to drill the holes in the door and applied tape first. I also went through my collection of drill bits to find one that would give a nice snug fit with the nutsert's I used for the installation. Worked fine.