The concept of placing a standard gauge box car next to a narrow gauge car to show the difference of size is a good one.
But, you don't have to do a hands-on demonstration of trans-loading the freight. A good sign about the size difference and how many ng cars it would take to equal one sg car would serve to educate.
Some pictures of how the movement of freight was accomplished would be a good addition.
Some railroads had transfer platforms between tracks to enable the freight transfer between box cars. Did the Rio Grande do this?
Brian Norden