Hi Tim,

Speedwitch makes a set for Seaboard 40' boxcars, but I'm not sure if it includes the gothic style lettering for the initials and numbers shown in the photo you reference.  It should include the herald and dimensional data, though.  You might be able to find a Champ Decal Co. alphabet set on eBay that would do the initials and numbers, or at least come close.

Todd Sullivan