how to take apart Lionel pasenger cars for repainting

The secret to getting these apart is to squeeze the windows in from the bottom or sides instead of trying to reach over the top... hold the car in front of you with the side windows facing to your left & right between your hands.

Press in on the "notched/raised" rear windows with both index fingers using a pushing up motion at the same time to "unlock" the raised tabs from the windows. Switch to the front windows and do the same. Repeat on back windows again... usually by this time you have opened up the roof enough to get a grip on the roof panel and raise it straight up & out of the car. Here is the Ploar Express observation(same tooling/method):

Don't mar the finish by using wedges or screwdrivers to pry the roof up - it just isn't necessary.

Only the earliest Milwaukee cars had the additional tabs in the undercarraige area - and yes, they must be clipped/excised to facilitate the roof removal.