Like SS said, it is pretty simple to make your own side windows from Lexan or Plexiglass, especially for a sedan, as the window is supported with the doors window frames. I made my own lexan windows for my 64 Falcon 2 door sedan, and my 78 Fairmont, I just bought a sheet of lexan, and using the factory door glass, traced out the pattern, and cut it out with a sabre saw with a fine toothed blade. On the Fairmont, the weight saving was not all that much, so I swapped back to the factory glass, but on older cars, with much thicker glass, the weight savings is fairly substantial.