Fred Jansz asked:"An OLD friend heard I was into US prototype trains and decided to give me an Athearn blue box 50' gon lettered for Pere Marquette.
Is this a car that represents a certain prototype and can be turned into something prototypical by yours truly or is it a candidate for the lower shelves of my closet?"
Out of the box, no. However, it can be used for kitbash fodder for certain prototypes. The Cocoa Beach Shake N Take used it as the basis for a series of DT&I gons. Here's a quick sketch by Tony Thompson, and you can find the project materials at the Shake N Take group.
This kitbash was inspired by one written up by Richard Hendrickson in Prototype Modeler - I'm having issues with the Model Train Magazine Index on my work computer, but IIRC Richard wrote up other conversions using this model in Prototype Modeler.