These models date back to the early days of N scale (late 60s / early 70s). They were originally tooled for MRC by Sekisui Kinzoku (aka Kato). However, the original tooling made use of some tooling owned by Con-Cor (for the core, roof, ends, etc) and said tooling was eventually turned over to Con-Cor under threat of litigation. The first Con-Cor production was actually in Japan. Later production was in the US.
I'm not sure what specific prototype these cars might be based on (if any), but 50' auto parts box cars of this type date back to at least the early 1940s. Built in many different shops, they all followed pretty much the same basic design.