A 3/4" flange should be left when cutting out the windshield. Don't make the flange bigger- it will hold the windshield off the car and impair fitment. This is a common, and preventable, mistake.
The stock windshield is a DOT-legal safety-glass unit, made specifically for the SL-C. It isn't a copy of another car.
For race use only, a windshield is available in Lexan. This is significantly lighter, and isn't legal for the street. The Lexan windshield can be trimmed for a closer fit in a way that the DOT-legal safety glass windshields cannot. And, of course, there is some bendability in the polycarbonate version.
The glass windshield is glued in as is normal practice in production cars. The Lexan windshield is normally screwed in to the flange. More details are available in the build manual.
The SL-C is available with two different types of side windows: a one-piece fixed window, or a similar two-piece window in which a small lower portion can be hinged or otherwise mounted to allow a hand to exit, as to pay tolls. The two-piece windows have optional hardware, but sealing is an issue, and the opening is small.
Here are some pictures of two-piece windows and some builder-supplied hardware. The tape on the windows helps make the two pieces clearer in these pics. Obviously, you peel that off before you actually install the windows on the car.
Some builders dispense with the hardware approach, and have attached the two pieces with "H" channel, to locate and seal both window edges.
Here is a picture of a two-piece window installed on an SL-C:
Note that in this picture, the lower part is left off- though this is a common way to run these windows, there are clearly security and heating/cooling implications with this approach.
Here's a picture with a two-piece window fully installed, with a custom extrusion to hold the windows together:
Here is a pic of a "normal" one-piece window:
Most builders find the one-piece windows simpler to install, as well as providing better overall security.
In later cars, the Lexan was improved with a scratch-resistant coating. Older cars may be upgraded to these windows.
If you have the older, tinted (but non-hardcoat, scratch-resistant) windows, scratches can be polished out with 3M Perfectit, starting with the coarser grades and moving up to successively finer ones. The newer cars with hardcoat windows (all but the first dozen or so cars) cannot polish any imperfections out as this destroys the finish.
A frequently asked question is whether the windows can be made to roll up and down. A careful look at the shape will answer the question, as the windows are convex in two planes, making it impossible to move them up and down in a fixed channel.
There is at least one SL-C with a one-piece passenger window, and a two-piece driver window, an interesting variation.
The rear window is also Lexan. It is designed to fit in the race tail without modification, but will need to be trimmed for the street tail. A small amount is removed at the bottom of the window, nearest the back of the car.
When you mount the rear window, a large flange is good. 3-4" is good around the top of the window near the roof, with about 2" along the sides. This makes the area there stiffer.
You may also bond in additional stiffeners to the rear clam if you see the need for more stiffness there.
Like the side windows, the rear window is supplied with a scratch-resistant coating.
Excellent resource on working with Lexan here.
Mounting the Windows
Most builders use small screws that go into tapped holes in the fiberglass, or into installed rivnuts. This method has the advantage of making the windows easily removable, at the cost of visible fasteners. It's also fast and easy.
An alternative method is to use traditional windshield mounting techniques. This involves using products like Window Weld or similar urethane adhesives to glue the windows to the trimmed flanges. This install process is relatively permanent, but has the advantages of no visible fasteners, as well as increased security --it's harder to get the windows out since there are no fasteners.
The urethane method also requires that the edges of the windows be prepped with a painted edge so the adhesive isn't visible.
The urethane method takes more time, and costs more as the cost of the adhesive and special paint for Lexan to create the edge that covers the adhesive is more expensive than the fastener method, but offers a more refined look.
Here's an example of a car with the windows glued in:
Note the clean look with a production car border and lack of fastener hardware.
Examples of the screwed-in windows are on this page, above.
Rear Window Vents
Available since Summer 2015, carbon fiber vents are a tremendous solution for venting heat from the engine compartment. All production mid-engined cars have had vents in the rear window area to exhaust hot air, and now the SL-C has an easy-to-install, very functional and attractive solution for our cars.
The vents are made of carbon fiber, and are extremely light, as well as very well finished. No painting, clear-coating, or other prep work is required to use these vents. Fiberglass versions are also available; these will need to be finished using normal paint prep techniques.
A complete set of instructions is available here