Walthers / Rivarossi offers an RPO, Baggage, Utility Coach and Utility Combine that are each 60' long - just like their prototypes.
Athearn makes (if I remember right) a 63' RPO, 67' Baggage, and 72' Coach that are prototypical length. They also offer a Diner, Pullman, and Obs car that are 72'...