Charlie b's layout

[Charlie B]

Dave, We had to add a pusher for one of the reasons the prototype does, and that was so the strain of the trailing cars did not pull the coaches over on the curves. What you may have seen in the picture was a pusher on a mail train, however, I don't know of any rule that prevented them from a pusher on a passenger train unless there was a restricted car in the train. Many cabooses were not permitted to be shoved by helpers so they were put on the back of the helper.
I can't find any images either, but even if it was against the rules, somewhere somehow in all the years Pennsy struggled on the hill you can bet there was a pusher giving a helping hand.