i'm pretty sure it could be ordered from factory with a pass side mirror, or it was possible to have installed by the dealership. there was also a cable adjustable driver side mirror that could be ordered.
I've never solved the Chevy II/Nova right side door mirror mystery. Some Fisher Body cowl tag decoders indicate passenger side mirrors in the 5th grouping, but I have never seen an RPO code for a passenger side mirror in lists of factory options, however, they may have been included in some option packages. They are also shown as an accessory, which means a dealer install. In later years, left and right door mirrors were part of the sport mirror option, but a stand alone right mirror was still not offered in any Chevy II/Nova. Anybody have more info on this?
Thank you for all of your replies. My '66 Nova is undergoing a complete frame on redo. Notice no "restore". I will have a few personal touches. Will be black from the orig. DD code. All lower rocker, fender and quarter trim deleted along with the passenger mirror that I could never get a clear view anyway. The car will be absolutely stunning when done. A master painter always helps! And he is.