the "big" RPO's like 54 and 65 were used on the passenger trains like the San Juan and Shavano, not on mixed trains. Mixed trains, such as the Santa Fe Branch used the smaller RPO's such as the 053 which was converted to MOW use many years ago.
To do a convincing mixed train, you need a combine or perhaps a baggage car and a coach.
I don't think 480's pulled very many mixed trains on the NG. Mudhens did though. Most branch line mixed trains disappeared in the 1930's.
One could do a historic re-enactment of the Farmngton Branch Mixed in the 1930's with 463 and a handful of freight cars, running in the middle of the night.....