B&O cars were modified specifically for "gypsum wallboard" loading in the 1950's when a large gypsum deposit was discovered near Shoals Indiana. Note that the Intermountain model has "Return to B&O RR Shoals Ind" lettering. Both National Gypsum (Gold Bond products) and US Gypsum(USG "Sheetrock") built plants in that area and the railroad built a long, long spur to serve those plants (can be seen on Google Earth aerial views).
These cars served other National Gypsum and USG plants around the country. I have a photo of two of these B&O cars with "Gold Bond" loads at Portsmouth Maine in the 1960's.
