Prototype information from Full Throttle:
After WWII, American Car and Foundry (ACF) designed a tank-type "Center Flow" covered hopper car to carry "modern" products. Here was a "Freight Car for the Future," ready to transport sugar, cement, sand, salt, fertilizers, many types of grains, coke, starch, feeds, chemicals and plastics!
A proponent of feed supplements for animal husbandry, Dale Wilmore McMillen founded Wayne Feeds and Central Soya producing a concentrate of soy protein, vitamins and minerals lacking in regular feed. Wayne Feeds merged with American Milling Co., a soybean crushing mill, in 1929 to form Allied Mills.
In 1894, William H. Danforth began producing feed for various farm animals under the name Purina Mills. The predominant brand for each animal was generally referred to as "Chow"; hence there was "Purina" Horse, Dog, Cat, Rabbit, Pig and even Monkey "Chow". in 1902, he merged with university professor Webster Edgerly, a producer of breakfast cereals, to form the "Ralston Purina Co.". In 1998
it was purchased by Koch Industries and in 2001 by Land O'Lakes.
Here are two covered cylindrical hoppers which carried these products to distributors across the USA.