These cars were built by ACF (American Car & Foundry) and have been around since the late 1960's. These cars are still widely in use today, along with several variations of the 3-bay and 4-bay hoppers they also have built.
Do yourself a huge favor and replace the MTH trucks with Atlas O 100T trucks- they are by far the best trucks on the market and will make this car look so much better than with the MTH trucks.