Not sure when they were added, but guessing sometime in the late 30's early 40's, but some maybe later (like the 473) or maybe added and removed for various reasons. I do not believe the K-37's ever had them but am sure someone will correct me on that.
They probably got you an extra ton or so and were problematic to maintain, especially in later years when front end loaders were being used to load coal, like in Durango. When I worked in Durango, they took a beating and were replaced as needed.
MDR