https://www.trainworld.com/manufacturers/walthers-ho-n/walthers-proto-HO-920-series/proto-2000-freight-cars/walthers-proto-boxcars-reefers-and-stockcars/walthers-920-108803-40-mather-stock-car-rtr-gsx-4010/
"The cars operated into the 60s when livestock transportation moved to trucks and meat processing facilities decentralized and shipped more frozen meat in reefers and trucks."
I tried to sell my two cents worth, but no one would give me a plug nickel for it.
I don't have a leg to stand on.
Suggest you query the New York Central Historical Society for info on GSX operations and history. The NYC handled the lion's share of New York City's meat and livestock traffic. The stock blocks were almost always handled right behind the power on the hottest hotshots on the road, running between Chicago and the big cities to the east. Green Frog Productions has DVDs by Emory Gulash entitled "New York Central Odessey" that show livestock cars on eastbounds into Detroit.
Another source of information is Kalmbach's book "Guide to Industry: Livestock and Meatpacking". New York Central's final double deck stock cars were 50 footers vs. the 40 footers P2K produced. They were leased from North American Car Company under NITX reporting marks.
P2K produced awhile back some lease stock cars, one in particular was letter for GSX. Anyone know a historical link that provides usage dates and territory covered by these cars?