That is a sharp looking car! One of the best parts of this hobby is how it allows us to relate to memories of our youth!
As for the "billboard" laws, as long as the cars were leased or owned and in captive service, the "normal billboard" rules wouldn't apply. Dubuque Packing, Needham Packing and Pepper Packing cars ran into the 60's. In my reality Borden's did the same thing. 
As for prototypical accuracy, I used to only buy billboard reefers if I knew they actually existed but I've since stopped and just purchased an item if I think it looks good. I'm lucky if 1 in 100 people would notice if they see it, and if they didn't and commented I always just comment "ABC Packing" didn't have those in real life, I just liked the look.
I know the Schmidt's car is a fantasy scheme as well just from the fact there never was a Pennsylvania Refrigerator Express.
-Greg
