For this project I purchased Bombardier Multilevel passenger car shells from Island Model Works.  These cars are not widely used throughout the U.S. and are special to NJ Transit because they can safely clear the old tunnels that go under the Hudson river into New York City.  Below is a picture of how they looked when they arrived.  As you can see there's a lot of flash that had to be cut out from the windows and along the bottom of the cars.  It took a lot of patience, but it wasn't too hard to do.

The picture on the right shows how I marked which way the chassis should face with a similar arrow on the inside of the car.  I also gave each chassis and each car a letter so I know which chassis goes with which shell.  This is necessary because the shells came with columns where you attach the chassis, but the columns came all the way to the bottom of the shells.  I had to use a Dremel to grind them down so that the chassis would fit into the shell.