That's a pretty nice AF Primer, Ed. You've provided a nice, general overview without getting bogged down in the minutia.
Seeing your collector friend wouldn't let you open the Pony Express box, here's what the locomotives look like for the benefit of the viewers:
The only disagreement I would have regards the MoPac set. The paint isn't 100% correct for the prototype. MoPac used light gray, where Lionel used silver. Still, it's nice looking:
Rusty