Here is another post on this Forum about mirrors. I recall that at least one other post maybe even two exist. I'll take a look and update this post if I locate them.
Rear view mirrors
I plan on making a support from 1/2" diameter aluminum rod that will mount to where the typical dashbord mirror mounts and to the top of the windshield frame. This will also help reduce any windshield vibrations. The mirror will mount to the rod and will be adjustable to whatever height it is needed between dash and top of the windshield.
Arthur
I'll post photos when I finish it.