"Well, RJ, I am in the process of building a model of a box car that was built in January 1942 as an automobile car. It’s definitely a 10’-6” IH car, but it’s even labeled on the side as a 10’-4” IH car because it was originally equipped with racks, reducing the clear IH by 2”."
I would check the notes within the ORER regarding the car you are modeling. The IH stenciled on the car would reflect the height at the eves (with the loaders in the loading position). With the racks in the stowed position the inside height would be reduced by 8 to 10 inches depending on the frame design of the loaders.
"So the railroads anticipated shipping automobiles in box cars at least into the early 40s.
They didn’t ship many, of course, because most auto manufacturers were converting their factories to make war materiel."
Automobile production was ceased in February of 1942. There were autos available to consumers for a few months, but they were sold subject to restrictions and rail shipments dried up quickly over the next couple months.