Before actually mounting the mirrors permanently I think it might be wise to temporarily attach them using some tape just to confirm that they can provide the adjustment necessary to be fully functional.
owners have used various glues to attach directly to glass. It should not be necessary to physically scratch the glass surface for increased adhesion, as some owners have done.
I believe others have used double-sided automotive trim tape
others have mounted the mirror base to a thin sheet of metal, correctly shaped to slide underneath the rubber gasket of the door “vent” window
The backside of the mirror mount plates as shown in your photographs do not offer very much flat area to meet with the window glass or a flat metal piece
I would explore how to provide a better glue-friendly surface to the mount plates
ideas that come to mind are gluing a properly sized sheet of plastic to the base, or fill in the backside of the mount base with a resin/plastic product to create a flat surface
Hope this helps a little,
Larry