August 21st, 2012.
Having been asked frequently to consider this project, I gathered information.
All of the USRA triple hopper cars were originally built with a "Clam shell center door".
Needing a higher level of maintenance, most of the clam shell design center doors and pockets were replaced within ten to fifteen years of their being built with the fimilar saw tooth center pocket.
photo courtesy of Al Kresse
photo R Y Models