I used motorcycle mirrors which have a 10mm thread on them. I bored out the nutplates and rethreaded them to 10mm. The mirror stems take the place of the rear most bolt holding the mounting bracket to the cowl. I had to source new bolts for the front of the mounting bracket in 10mm as well as I wanted all four to be the same thread.
To change back to a windscreen I just loosen the lock nut on the mirror stem and wind the mirror out, remove the other two bolts and its off. I can either use the mirrors with the windscreen or add two more bolts.
Shown here with the windscreen in place.
http://usa7s.com/vb/attachment.php?attachmentid=2922&stc=1&thumb=1&d=1301722917
BTW, with these mirrors, the windscreen and wind wings, the buffeting was reduced from that of the windscreen and wind wings alone.