Did you ever sort out your query about the rubber bumpers that position the sidescreens? They are shown clearly on pages 43 and 48 of Rinsey Mills' Original Ace & Cobra and are, to the best of my knowledge pretty standard on all Aces and Cobras, whether flat or curved screen. Certainly my Ace 2.6 had them on its original flat screen, and the curved screen that I swapped that for had them also. Or should I say it had the brackets: the rubbers were missing, with the result that the sidescreens clatter horribly on bumpy roads. I have not found a source of these rubbers, so if anyone is interested in getting a batch made, please let me know.
The part of the rubber that does the work is shaped like the frustrum of a cone, while there is a long conical piece that you push through the hole in the bracket to locate it.