Appreciate the collective commentary/ suggestions. Seriously! In reply, and not in order:
-- I have glued one windshield in place "deployed" or "upright" already… However, am probably going to glue at least one other "down" or "flat." Am now thinking of painting these a dark grey with some kind of highlights as if reflecting light… In fact, as I left my office on campus today, I actually paid attention to what windshields and windows looked like (reflective? opaque?) at about 75 to 100 yards, ruling out the obvious disqualified (anachronistic) cars, trucks and SUVs with tinted glass. I also like the idea of simulating the "swath" of clear glass left in the wake of windshield wipers -- but NOW I will have to determine if the S20TL wipers were mounted on the bottom of the windshield (like most cars, for example), or the top, as on American Willys' Jeeps?
-- I find the idea of scratch-building a frame to which to glue some clear plastic cut from a WG or other company's blisters rather daunting. I LIKE the idea -- I just think it's beyond my skill (and fumbling fingers) at 1/56 scale!
-- NOT beyond my skill, not as such, has proved to be a variation of the last idea. With a brand-spanking-new blade fitted in the trusty Xacto handle, this evening I carefully "cradled" the windshield of my second S20 on a double-folded hi-quality paper towel. This provided the resin piece the chance to "give" when gentle pressure was applied, and also some stability at the same time. I then CAREFULLY scored the two "panes of glass" until they came away from the frame. I should now be able to glue a piece of clear plastic behind the frame (i.e. on the driver's side), and there you go -- well, uummm, there "I" go! I will probably paint thin lines corresponding to the frame along the back-side of the plastic (driver's side) in the same color as the rest of the vehicle, so that it gives the hint that the "glass" is in fact fitted into the frame (not just "resting" on the back side of it!).
-- HOPEFULLY, I will be able to do this for the windshields of the two remaining S20s and one S15 currently in my collection!! I think this is the way to go… I think so, even for the model on which I am thinking I might glue the windshield in the "down" position.
Again -- sincere thanks for all the suggestions! They did help me crystallize my thoughts!