Actually, the Merci Train was sent by the people of France to the United States in 1949, in gratitude for American donations to France in 1947. The ship bearing the 49 "Merci" boxcars arrived in New York on Feb. 3, 1949. Contained in the cars were many items donated by millions of French citizens, including dolls, toys, statues, clothing, furniture and other personal items.
The carbody for sale in Wisconsin may well be a car built in the U.S. for service in Europe during the Wold War I period, but it isn't one of the French "40 et 8" boxcars. During Wold War II, several American manufacturers also built boxcars, flats and gondolas for use in Europe. They were delivered as knocked-down complete kits, with wheels and everything, and were produced in four-wheel and eight-wheel versions. A couple of the boxcar kits somehow wound up at Cass Scenic RR in West Virginia, where one is in use today as a sandhouse. I've also seen a couple of the larger boxcars in a junkyard not far from my home. A preservation group in Holland has assembled an entire train of the USATC "freight wagons," with a USATC four-wheel diesel locomotive at its head.