I've heard of the eagle rock in a few old blues/ragtime/boogie songs from the 30's. And Ballin' the Jack was referred to in a Chuck Berry song - I don't remember the title, something about school days. The line was "we were balling the jack, but were all back in place when the teacher got back."

As for trains, could it refer to the governor mechanism on a steam locomotive? There were two steel balls on a centrifuge-type mechanism. When the balls swung out to a preset point (controlled by the engineer) by centrifugal force, it would automatically decrease the power, thus maintaining a constant speed. I believe the expression "Balls to the wall" meaning full speed came from this.