Here are a few pictures of my new Lionel Heavyweight Pennsylvania Diner with the green windows removed and replaced with clear plastic. The plastic came from a Walthers Clamshell box for Modular Building parts. Any clear plastic will work. Transparency sheets from Office Max would do.
The four 1/16" square LEDs were painted Testor's "International Orange", then I adjusted the brightness by removing some of the orange color by scraping some paint off the LED. (Tamiya "Clear Orange" could also be used. I used what I had.) The car is now dimmer, yet not orange. The green aquarium effect of the original car is gone. I did leave the green window on the Kitchen section because there is no interior in the kitchen.
Sincerely, John Rowlen