Paul - The top-side window material is a plastic film with a mottled white and blue treatment hand-applied to it. Reproduction machine-printed material is available but it is a bit thicker and less translucent then the original. If possible (and it usually is) one should try to recover the original material for re-use. Like the clear plastic window material, it is held in place by a few sharp-edged tabs.
When I get around to working on this car I'll need to add a pick-up to one of the trucks to provide current for the lighting. The earliest versions of these cars had no installed lights...they were lit by a string of lights that could be purchased separately and run through them from a connection on the locomotive. I've only ever seen one of those kits manufactured by Lionel. The 33 that I have has the connecting post but it is not wired into the loco.
Here's a pic of what the kit looks like:

Paul II