The ones on your Dart look to be the twin post manual mirrors, correct? My understanding was if you wanted a RH mirror on a '67-9 model, you had to have a remote LH one. What part numbers do you have for the mirrors? I have a factory parts manual and only find two mirrors listed.....the manual mirror.... and the remote mirror....both driver side. They do list a 3rd mirror but it is supposed to be for a Police car only so we won't go there! :-) The only RH mirror I find in the '66 parts manual is for an Imperial. Do you have a copy of your broadcast sheet that shows a RH mirror?
