This model dates back to the early days of N scale (late 1960s). Atlas was the original importer. Walthers imported them for a brief period of time during 90s (in Roco packaging).
I don't know what specific prototype this model might be based on (if any). However, it does share similar characteristics with the composite gondolas designed by the USRA during World War I, so I guess it's probably safe to assume that it's from around that same era.