Ouch, the GG1 is painful to look at
I agree that coach is a very good match for the GM&o's, really good looking train there, do recall the name of the guy in Alabama who allegedly got it from Smith? it wasn't Joe Fiore was it?
Ok, so this is a stretch as it’s not per se a passenger car, but if we’re doing RPO and baggage-express cars let’s broaden the topic to other head end equipment, as in it’s got steam lines.

Weaver troop sleeper with what I think is NYNH&H’s or maybe B&M's door configuration, whichever Weaver apparently thought would be the most representative for the post-war troop-pullman conversions to insulated express cars. They(weaver) did a bunch of them in a variety of REA and common carrier schemes.
This one has been painted into a late era REA scheme, one of a 100 car series REA leased from Chicago Freightcar Leasing, hence the CRDX reporting marks. I saw a lot of these cars on the IC’s secondary express trains with this big X REA scheme, actually pretty commonplace in the 60’s everywhere until Amtrak. As I recall this one got done with Floquil BN Green and a late model Walthers decal set.

There was quite a variety of variations around the side doors, windows etc. depending on the railroad. I have a similar NYC car in black that has torn itself in half thanks to the zinc pest issue common to their die-cast chassis. I got a replacement for this one from Atlas about five years ago, alas their last one in stock at the time, so the NYC car remains bisected. I have to see about getting two more as well. Switching out the cast floor was a bigger challenge than I expected as well.