There are kits available but I have no idea how they work. I did mine as a non show car, race only swap.
I cut out the seal lip and slid the Lexan under the body skin then secured it with plates riveted through the body skin. Close up you can see a few of the rivets around the window.
I made supports on the rear roll cage tubes to help hold the Lexan up. At the rear is some aluminum channel that the Lexan slides into. Because the window is under the body skin, no air can get underneath it.
I then fabricated a sheet of aluminum as a deck lid which covers the aluminum channel. The deck lid is attached with Dzus fasteners in case I need to access the battery.
Because the rear window doesn't have a frame, the Lexan will need to have some way to keep it's shape if used as a direct replacement. You would need an oven big enough to put the whole sheet in to mold it into the proper shape. My rear window is 1/8" thick which is very easy to bend but offers no support.
The back window and deck lid are very heavy but it also puts weight over the rear wheels. Changing it to Lexan makes a nose heavy third gen even more nose heavy.
Here's a complete premolded window kit. It's only $1100. The unmolded kits are $490
http://www.jegs.com/i/Percy%27s/760/01137-22/10002/-1 http://www.jegs.com/i/Percy%27s/760/8-01137-22/10002/-1 
