Thanks Everyone,
I ended up following ZPL955 links advice to mount 1" further back than the Left hand side mirror. On a 68 that's fine though I suspect it may be in the way of the vent window for a 67.
1- YES, have someone hold it where you think it should be and be sure it's right for you.
2- Cover area with tape and the outer area with rubber or anything that can take a drills head slipping across the surface. Not worth the risk otherwise.
3- 1" further back than the Left hand side suits a 68 and still looks symmetrical when looking at car from the front. Further back may not but personal choice.
4- Aftermarket metal thread screws hold the mirror well enough though there is a upper reinforcement/brace a few mm past the door skin if you wanted drill through to that and use longer screws. You would have to be careful they are not too long and reach the window of course.
For anyone searching for this in the future....
1-
Original left hand side door mirror hole measurements are thus... {in millimetres as it's often Aussies looking this up I reckon
} I then replicated these and moved 1" (25mm) further back for the right hand side.
2-Straight line from centre of rear hole, through holes to front edge of door = 152mm
3-Straight line from centre of front hole, lined up through both holes to front edge of door = 110mm[/li][/list]
4-Distance between hole centres = 42mm
5-Front hole centre to edge of chrome trim = 22mm
6-Rear hole centre to edge of chrome trim = 20mm
* NOTE. when replicating these measurements to the right hand side THEN moving back 1", the distance from hole to chrome trim seems to even out to about 20mm.
While I was at it I covered the original remote mirror hole on left hand side with quality tape to reduce water entry. If you leave a 1-2mm edge it will hide under mirror base.
