The above side mirror on the 58 red car is an adaption of mine which is identical in the stem, except mine uses a Lucas rectangular mirror head instead of a round one.
The idea was to cut the head off the Dzuz and bronze on a stem from a motorbike handlebar mirror. The stem comes with the finisher nut that tightens the mirror against the staunchion, after it's engaged with a half turn. This makes it pretty much theft proof.
The challenges were to attach the stem to the Dzuz so the mirror was correctly positioned when fitted up. It had to be clear of the sidescreen when the door was fully opened, and be in the viewing area through the perspex window.
Keith is a skilled engineer who has drilled and tapped the Dzuz, and turned down and threaded the stem, so it's easier to adjust the stem to the correct position.
Moseso, that probably answers your question, and I'll ask Keith tomorrow if he'll fill overseas orders, and post the answer.
Regards,
Viv.