The Barringer Library has posted several interesting steam era freight car ACF builder photos in the past week, including ATMX 1000-series helium cars under construction in 1955, USN 100 twin hopper from Lot 3425 in 1949, and RDG boxcars from Lot 3469.  From this link you can browse the images:

https://www.flickr.com/photos/barrigerlibrary/35034446102/in/photostream/

Andy L.
Cedar Rapids, IA