I found a set of diagrams http://southernmodeler.info/SRrollingstock/SR_FRT_CAR_DGMS_1969.pdf
and on page 305 out of 312, I saw a car that caught my eye, so I designed it. From what I can tell, SOU did have one - numbered #4999, but they had ONLY one. We have been unable to locate any photos of the proto. Little did I realize that I had selected a unique (one-only) car.