Does anyone know if the C&O had box cars lettered with Railway Express Agency AND Chesapeake & Ohio? Or were REA cars not labeled with their respective carrier names? See below. Thanks, Doug 
Well, in general, the only cars I’ve seen with both REA and a railroad name on it were baggage - express cars where part of the car was used for baggage for the RR’s passengers and part was used for REA express parcels. I’ve seen REA express boxcars but they were just lettered REA, not also with a railroad name on it. I have seen railroad-owned boxcars labelled “mail storage” or something similar that was used to carry mail in a passenger train though.
Of course that doesn’t mean it didn’t happen somewhere sometime, but if it did, it must have been fairly rare.
Yes C&O had express 40’ boxcars painted as you have/ They were numbered in the 200 series. Right off I can’t tell you how many but it was only a few. I can’t vouch for how accurate the lettering is without looking it up, but it is pretty close if not exact.