First of all, removing your old divider window will be a major PITA, but maybe that was just me. The SM makes it look easy of course
Your have to remove all surrounding interior pieces (easy), the seats (easy), and then I used multiple new, sharp, and long utility knives (razor blades) to cut from the inside of the car all along the window rubber and foam sealant until the window was free.
Then, once it's free, you need to clean up and try to scrape off remaining rubber gasket material. I imagine installing a new OEM replacement would be easy after that, but I went with my lightweight racer theme and decided to fit Lexan.
So, I went to Home Depot and bought a huge sheet of UV-treated lexan, cut it out and then drilled/bolted it in with some weatherstripping. It turned out pretty nice IMO, but was a lot of work. Also, engine noise will BE LOUD, and the Lexan will scratch easily so you need to be carefull when cleaning it or just polish it a lot.
Personally, if you have a quiet exhaust and like it relatively quiet, do not replace it with lexan. I would even question if you would want to replace it with the single pane Zanardi glass either then. You may want to ride in a Zanardi to find out.
Here's my thread with a little more info:
Wow - I've had this on for almost two years now! I used stainless cap screws, washers, and locknuts, and also fitted small rubber washers under the stainless washers that fit up against the lexan. The cap screws are not torqued much - don't want to stress the lexan unnecessarily!