I made brackets that fit behind the mirrors, and used existing fairing screws to mount. I made mine out of .125" aluminum plate, and mounted them so they would exit below the mirrors. I did have to trim a small amount of plastic from the bottom of the mirrors.
I will look to see if I have some old photos. I don't have any measurements. I just pulled the mirror and made a cardboard template. I used the template to rough out the aluminum mounting plate, and then just fine tuned it to fit the way I wanted it. Then made a twin for the other side.