First you will need blue prints, I found a 70′ at http://www.shiawasseehistory.com/images/mckp2.jpg and a 55′ at http://www.shiawasseehistory.com/images/mckp1.jpg some others are online. After saving the picture, then open publisher and stretch the picture so that the car is 18.9” for O scale or 10.395 for HO scale.  Then print out the picture and glue or tape it to the metal.Do the same with the base, size the paper to the exact same length as the body, Then cut around the edges with Wiss snips or sheet metal cutters, then file the edges.  Make sure the cuts are strait or the body will warp.