Congratulations - you’ve found a very distinctive car there!
My patent-pending quarter windows are mounted on frames made from mild steel, 16 gage, half-inch box tubing. They’re flat, and two out of the three tubes comprising each frame are straight. The bends were made at home on my workbench – I don’t actually have any memory of how I made those two bends so it couldn’t have been too difficult. At the time I made them, I didn’t have access to welding equipment or even an oxyacetylene torch, so I know I didn’t “sand bend” them and I’m pretty sure the steel was cold when I made the bends. It’s a big radius, so there was no significant buckling.
I had the car stripped-out at that time for installation of the rollcage. I hired a local welding shop to do a bunch of welding for me at that time – they welded in the mounts I had prefabricated for the rollcage and they also welded in the mounting tabs for the windows’ Dzus fasteners. (A different shop that specialized in building circle track racecars bent my rollcage tubes and welded them in.) My local welding shop also welded-up the three corners of the window frames (where the Dzus springs are mounted.) Their TIG welds were nice and flat, and I barely needed to smooth them on the glass side with a side grinder.
The polycarbonate is mounted to the steel frames with 3M (double-sided foam) “Trim Tape”. That stuff is great! It’s been holding strong for almost fifteen years now – through rain, shine, heat and cold. It’s even made exactly the right width. (I personally wouldn't want glass quarter windows on account of weight... but the trim tape would probably strong enough to hold glass in this installation.)
Before assembly, the steel frames were painted (actually, the whole car was...) and also I spray painted the polycarbonate. If I had it to do over, I’d paint the “inside” surface of the window instead of the “outside” because it would look much better – but I was concerned the tape might pull the paint off the polycarbonate. In either case, the purpose of the paint is only to conceal the frames and Dzus fasteners. The paint I used was especially made for automotive plastic – the guy who painted my car had a half-used can and he just gave it to me for free.
One of the tricks to these windows is using the right trim seal for the job. This isn’t exactly what I used, but it’s pretty close:
(Note: the second
one down... not
the first one.)
On my installation, the polycarbonate extends beyond the steel frame a little bit all the way around. The rubber trim seal bears against the steel frame, not the polycarbonate. Dzus pins come in various lengths, and I selected the length that would pull the windows tight into the foam rubber sealing strip all the way around the windows. The Dzus fasteners are only accessible from inside the car. I sewed a padded bag to protect the windows when they're not installed, and I made a bracket to store them on the bottom of the GT's plywood cargo compartment lid - but now that it's been removed I find that they stash pretty neatly above the battery boxes.
Before I made these windows, I had polycarbonate windows that were pop-riveted in. If you go that route - racecar style - be aware that the mounting surface needs to be very flat and hard, or else the rivets will pull the polycarbonate into a distorted shape and they'll look like hell. Sheet metal screws might work better in that respect, but I prefer trim tape instead of either rivets or screws.
Don't substitute acrylic. IMHO, it's too brittle.