I think they were offered in a towing package. Its been a lot of years the non tow package had door mounted drivers mirror with r/side optional.Spot on. That a 1964 Bonnie. 389 or 421.
They had the funny, wide stance windshield wipers until later.
The fender mirrors should be round, not rectangular.... I thought they came with only driver's side, maybe passenger side was optional?
Late 50's to mid 60's were the car we worked on when I started trade school in 71. Very easy cars to work on.