As N&W said, they were stream-styled heavyweights. They had full diaphrams added and really only worked well as a set. There are pictures of the cars in other trains later, after they were broken up, and the height difference over a streamlined car is very noticable.
The Key cars are very heavy and don't roll all that well from what I understand. Also on the Key set, the full diaphragms are just there for looks. I have drawings of an attempt to make them work. The cars will magnetically couple through the diaphram. It's one of those ongoing projects that never seems to move forward, just like the P7D to pull them.
