Bob, you are correct about the flange. Matt did mention it in his post.
"This also means that the flanges on scale wheels are farther out than on a hi-rail wheel."
Same meaning just a different way of saying it.
I noticed that the flanges were not the same on 2 rail and 3 rail equipment when I tried to build a display case that would have grooves for the flanges. I wasn't easy but eventually I found a happy medium that worked with both types.