I had a photo of a B&O EM-1 sitting on a service track hooked up to a Blue Bay window.
The requirement for the Caboose with EM-1 was simple. They needed to be Steel to withstand the compressive forces when a EM1 is shoving.
I own a number of Beano cabooses and PRR cabins as well. Most are steel with some wood ones in the mix. As far as I am concerned I will hook an engine up to a caboose and have fun.
Cabooses were assigned to a Conductor. Not the engine. Correct me if I am wrong. Some were in Pool Service.
The EM1 is a good engine, I hope to own one someday.