[Marshall V. Daut]

Buy a cheap ping pong paddle with the pimply rubber faces. Try for a dark color, or even gray. Peel off one side of the rubber pad and trace the shape of the windwing brackets on the smooth side of the rubber. Then use a pair of scissors to cut out the eight pieces (four per side). Glue the smooth side against the metal clamps and allow to cure. This leaves the pimply side facing the glass, which will provide a little more grip than a smooth piece of rubber. When compressed, even a little suction action will assist as the air in the small open areas around each pimple draws against the glass. As recommended above, use a couple drops of Crazy Glue (NOT Gorilla Glue, which expands as it cures!) to each pad, slip the glass in between the clamps and then tighten the screw in each bracket. Be sure to back the serrated little tension screw out a ways beforehand. This puts a tilt in the outer bracket for added vise gripping power. It helps to have a friend hold the glass while the glass is placed between the bracket halves and the screws tightened.
Another tip: don't do this with the convertible top in the up position unless you have previously marked the brackets' location on the glass with a marking pen. If you don't do that, once the top has been put back down over the windshield posts, you might find that the glass is either too high (hitting the top's edging) or too low. Make sure both sides are even in height and adjusted for appearance and function.
Yes, it's a pain to mount these things so that the glass doesn't fall out. But Ford managed to do that in hundreds of thousands of open cars, albeit with better clamps and rubber pieces designed to anchor inside the brackets. 100 years later, we modern men should be able to come up with a solution to the Repo Parts Blues and secure the glass pieces inside their brackets.
A final note: Do NOT use regular glass! Pay the extra money for safety glass. You may wonder why I state this obvious fact. I have bought Model A's, whose previous owners took the cheap way (Surprise!!!) and installed regular shelf glass windwings. I still have the scar where one broke while driving on the highway, its glass shards flying back into my left arm. Ensure that you are dealing with safety glass before going through all the above steps. Or you'll have to do it all over again with the proper glass.
Marshall