Was asked the other day for the measurements to locate where the exterior mirror was located/attached to the drivers door.
Took some measurements and provided the following. Hope this will help others with a need for such information. Note - don't know if the installer was provided a template or did it free hand but two unrestored 66's were available and the measurements matched and were used for the illustration below. If they are printed too small to view let me know and I'll redo that and repost
Measurement is to the forward mounting hole and the gasket can be used as a guide for the second hole.