First -- thanks to all for the encouragement!
John Golden asks:
1) Can you tell us a little more about the prototype? Who built these cars, and were similar types built for other companies?
2) Are the decals the new ones from K4?
1) I have little native knowledge of these cars, but there's quite a bit of background along the lines you ask in the four references listed in the original post.
2) Yes, the decals are K4. They are slightly oversized (obvious when comparing their length vs. prototype photos), but otherwise very nicely done. Not something I'm losing sleep over.