A big security compromise, especially if the car is still road-legal and used as such. Of course for race cars, it's de rigueur.
If you were to use Lexan Margard, you could retain the original look and functionality, and still save weight
The Lexan Margard suggestion enables just that - scratch-resistant lightweight windows that you can roll up and down...
P'raps a scrapyard is your best bet for Manual Window mechs?