I may be in the wrong forum because I'm a Jaguar enthusiast, but I've been there done that: I installed Electric mirrors (YES) in my 1965 Jaguar S type. I got them from a modern Jaguar XJ-6 including the XJ-6 switch. Can't live without electric mirrors, especially in today's traffic conditions. It's a safety issue.
What I did in order to duplicate the driver's side mirror holes to the passenger side door, was to cut a cardboard template of the driver's door mounting holes and front-of-door edge shape, then I inverted it around and used it in the passenger door. Turned out perfectly. But if you make a slight mistake, one of the holes can be slightly enlarged and that usually resolves any problem. Just do it slowly, don't rush.
attached is a photo of the Driver's side XJ-6 electric mirror in my '65 S type. Incredibly, the XJ-6 mirror follows the door contours of the S type perfectly. Some things never change.