Even earlier were Santa Fe Ft-W flats (GSC) with bulkheads delivered in 1952 -- 38 cars with 10'0" bulkheads. GM&O was an early adopter too, 50+ cars by 1953.
The Santa Fe began applying end bulkheads to existing flat cars for gypsum wallboard loading immediately following WW II and by the early 1950s had many cars assigned to that service, owing to the postwar building boom in California and the southwest.
