Lexan Sliding Window F40s

I would like to understand the history of the F40 cars with Lexan Sliding Windows. How many were made? Were they just made on the early cars or were they available at anytime in the production run? How much weight did they save vs the glass window cars? Were they only available in non cat, non adjust cars? What other facts are know about these cars? It seems these are the most collectible version of the F40, is that correct? How much of a premium is.a Lexan Window car worth over a Glass Window car?
Thanks!