If you are one of the lucky ones that have the full 12-car El Capitan set this may be of interest. The Santa Fe Railway had a very specific order for the 12-cars. This was policy strictly enforced.
For Santa Fe El Capitan circa 1956 was always run in a very specific order. That being:
Baggage (storage mail)
Baggage
Baggage-Dormitory (transition car)
Hi-Level 68-Seat Step Down Chair Car (ran backwards)
Hi-Level 72-Seat Chair Car
Hi-Level 72-Seat Chair Car
Hi-Level Diner
Hi-Level Lounge
Hi-Level 72-Seat Chair Car
Hi-Level 72-Seat Chair Car
Hi-Level 72-Seat Chair Car
Hi-Level 68-Seat Step Down Chair Car
I have been told, on VERY GOOD authority, that the storage mail car was run directly behind the power and in front of the baggage car for additional security.
The RPO's and Baggage Cars listed here were a pool shared by all ATSF passenger trains.
Budd 63' Railway Post Office #89-98
Budd 73' Baggage Car #3500-3554
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Here are the number ranges for the entire El Capitan fleet.
P-S 85' Baggage-Dormitory Transition Car #3477-3482
Budd 85' Hi-Level 68-Seat Step Down Coach #528-537
Budd 85' Hi-Level 72-Seat Coach #700-724
Budd 85' Hi-Level "Sky Lounge" #575-580
Budd 85' Hi-Level Diner #650-655
The Santa Fe made no distinction between the Step-Down Coaches used at the front of rear of the train. The tail sign and red light were not fixed items and so they could be used on any of the 10 Step-Downs.
As you can see there are enough cars for 5 complete 12-car El Cap trains. That is because at any given time there were 2 westbound from Chicago to L.A. and 2 eastbound L.A. to Chicago. The fifth set was being serviced in one or the other terminus locations.
FYI - the entire El Capitan was WYE'd at both Chicago and LA to assure that the order of the "El Cap" cars remained constant.
The Santa Fe took great pride in their Super Chief and El Capitan trains. Therefore, by insisting that the cars always be assembled in the same order was just another detail to maintain consistancy.
I can't speak for other railroads, so you guys can insert your RPO's where ever you choose, I'm just telling you how the Santa Fe did theirs.