The MTH car is a pretty car, it is a 50' car and PRR did have 50' Merchandise Service cars, but a PS-1 boxcar is NOT a scale stand-in for a PRR X40b. Here are photos of the prototype.
http://prr.railfan.net/freight...ane.jpg&fr=clX41
http://prr.railfan.net/freight...ane.jpg&fr=clX41