According to the informative brochure available in a little container welded to the truck, it is this car, built when Robert Todd Lincoln was president of the Pullman company. (I snagged a copy of the brochure for garyomaha.) Not sure of the significance of the name "Fred" carefully lettered on each end of the car.
We also found an old BN caboose and some miscellaneous militaria across the highway.
As usual, more at the Flickr set.