These cars have the thin large "SOUTHERN" and numerals on the sides of the car similar to the three bay hoppers in the 360xxx series. This thin style of letters and numbers is difficult to pin down.

Did Southern keep stenciling diagrams of the various freight car classes, such as this one from the NWHS archives?

https://www.nwhs.org/archivesdb/detail.php?ID=93862

If lettering guides per class were not kept, was a standard diagram of alphabet and numerals used by Southern published for car builders to use?

Ryan Harris
Fort Worth, TX