Early Dart companion mirror location

According to the sales code book, sales code #537 Mirror - outside RH manual
for 1966 so they were available to order from the factory. I looked in the service manual but didn't find any info. There was a diagram as to where to drill holes for a radio antenna.
I only see the 537 RH mirror code for the '67 and newer models. Maybe it was available real late in '66? What's the date on your sales code book?