LCT,
It may be easier and cheaper to have the right side ell brackets and arm made and then buy two matching mirror heads. The mirror head you have now doesn't look original, it look to big.
Before going to the trouble of making a right side bracket and arm you might want to confirm the support bracket with the captured nuts is installed inside the door. Take the door panel off to confirm it's there. If it's there you can take a centering punch and put it through the nuts and give the punch a light tap to mark where to drill the holes from the outside.
Take care!
Mike B
