Joe,

I use mirrors from an LT series truck on my '86 Westy, which _almost_
meet your spec:  two holes are required on the upper door frame.
Other than that, the mirror support folds forward/back  and the
mirrors give a tremendous field of view.

I think with some imagination a clamp of sorts could be fabricated
but then maybe the clamp would give way under impact rather than the
support folding...

Whilst LTs aren't available in the US, maybe parts could be obtained
via dealers/list suppliers??

HTH

Rich Lumb
'86 Westy MV