I did some research on the Red Arrow a while back and I believe the train was an all Pullman overnight express prior to WW2, and mostly Pullman with some coaches after WW2. All PRR heavyweight cars prior to about 1947 had no stripes, but when they started ordering new lightweight coaches in the 3-stripe scheme they started a repaint program for the HWs to also be in the 3-stripe scheme. It took awhile before all the HWs were repainted.
Lionel's Red Arrow set and commuter coach set represent the older, no stripe paint scheme. Also, the cars in the commuter set are suppose to represent PRR's P70 coach, a very numerous coach type with 4-wheel trucks.
I think Lionel's three coach set would be a good fit for the Red Arrow set if you are modeling mid 40s into early 50s. To bad Lionel didn't make an add on Pullman for the Red Arrow set to balance out the consist.