Thanks for all replies. Jimboylan: You may have read the same or similar historical info on the initial introduction of commuter cars of the "p54" design. They were built to be hauled by nonelectrical engines or by electrically powered units. I have read that there were mail and baggage combine p54 units on some commuter trains.
To clarify my question: Regarding the mu p54 cars hauled by engines (steamers, GGs, diesels) did those consists ever include the 70 foot headend cars?
It might be a rare instance. However, depending on necessity and availability of headend cars it might have happened. Just curious because I have read that types of appliances such as trucks, brakes, weight, mixing "p54" cars in trains was somewhat complicating.