Not wanting to build any kits, I find there is not much available to put together a Congressional Limited Express (CLE) using scale length (80') HW cars. There were no sleepers on the CLE, only coaches, parlor cars, diner, and obs (the time between DC and NY city was less than 4 hours). GGD P70s are correct for some/maybe most of the coaches, but I don't know of any correct non-P70 coaches available (unless they were the P54 cars). Get the GGD PRR HW diner/obs two pack for those cars, but they are very hard to find. The missing link for this consist are parlor cars; I don't think any 80' HW parlor cars have been made (again, no kits).
The minor problem with the GGD cars is they have the 3-stripe paint scheme. PRR's HWs did not start to have the striping until the late 40s.
If there were some 80' parlor cars available, I would consider buying the DGLE/5-strip version of Lionel's 4800 for this train.
ADDED: If you are looking for 18" cars, Lionel's Red Arrow set (6-25635) and commuter car set (6-15554 and 6-15558) would make a good looking no-stripe heavy weight train. The commuter cars even have 4-wheel trucks like the P70s.