Early Dart companion mirror location

You could just measure your drivers side mirror and match it. First, you'll have to decide if you want to look through the vent glass or door glass. It's just that it might look strange if you mount it back too far. Sit in the drivers seat and have someone hold it in place and see if the same measurement that the drivers side has, will work on the passenger side. Make sure the vent glass operation is not blocked.