Re: Ann Arbor Box Cars
The 1956-built AA 300-399 series PS-1 box cars with 6' doors went to the Baltimore & Ohio sometime after 1964 (Now we're out of STMFC scope). Not being particularly knowledgeable about the B&O, I'm not sure what number series they became.
Best regards, Rob Adams
Modeling the CB&Q RR's Keokuk & Western branch, along with connecting Wabash and CRI&P operations, circa 1938