I'm a BIG fan of including 'foreign cars' in regular consists. I can't speak for the Eastern or Mid-Western roads, but the Santa Fe saw a decent amount on foreign express cars in head end consists, as well as foreign sleepers, although they tended to protect their through sleeper service with their own equipment.
The Santa Fe saw headend cars from the Erie, NYC, PRR, ACL, MoPac, Katy, Rock Island, B&O, and, of course REX, among others...interchanged at various points along their system, but mostly Chicago and Kansas City.
I'm partial to this particular series of cars (built from PS supplied 'kits' in Santa Fe's Topeka shops-they were also delivered as 74' kits), so seeing them on foreign roads is pretty neat...
This is a beautiful casting by Bill (I'm working on 3 for my ATSF 'Fast Mail'-and have already determined that I 'need' another!)...I'd love to discover that the Santa Fe saw, in head end consists, OTHER types of cars that Skytop Models produces!
Respectfully,
~Bruce