I think everybody is a bit confused here. Most of the photographs actually depict the standard 42'6" flatcars that were used in Caterpillar service. From what I have been told, GM&O listed them as 41' flatcars because they measured to the edges of the wood deck rather than total usable space. There are one or two photographs in that list that are not GSC cars, but probably more likely depict rebuilds of cars from other builders. I don't see any 53'6" cars in the photo group.

ExactRail's GSC flatcars are the correct model to represent these.

Josh B