After doing some reading, it was a dealer installed accessory.
The '68-9 mirrors do seem to be side specific but are different from the '67 and without a vent frame, they can be mounted further forward. I looked at my left door and the holes in the right are about 1" further back, so I will keep that location, but weld up the back hole. They are spread too wide for a stock mirror mount anyway and I will align it perpendicular to the window ledge.
After driving semi for 40 years, I use the side mirrors way more than a rear view inside a vehicle. Something about having a wall right behind a person from a trailer necessitates learning to use the side mirrors...
Thanks for the replies, guys. Always learning new stuff about a car I have owned for 18+ years.