"These look great. Any chance GGD will make the missing baggage-dorm and a baggage/mail-storage car to go with it to make it more complete?"
It could happen, send Scott email with your interest. I have done so. The cars (and their names/numbers) that GGD offered were from the 1947 Empire Builder, with the domes from 1955, not realizing the other train consist changes in 1951 and 1955.
IIRC, the baggage-dorm car was one of the 1951 changes. The baggage (storage mail) car was a streamlined head-end car between the locomotives and RPO that generally appeared only in the Westbound EB, and returned east on Train #28; this storage mail car had a "GREAT NORTHERN" letterboard, not the "EMPIRE BUILDER" letterboard, since it was in general service. (Express boxcars in the EB consist were extremely rare.)
For those interested, the book Great Northern Color Pictorial Vol. 4 by John Strauss has an appendix which lists the Empire Builder car assignments over the years. I have no doubt it is correct, John was GN Traveling Passenger Representative on the train for 15 years.
While I am slightly disappointed the GGD consist wasn't accurate for 1955, these cars were too nice to send back!!