Thanks, everyone.
Jerry, Chris, I didn't say so, but I was thinking about the steam-era GW when I posted the question. Thanks for the offer, Jerry.
Bill, thanks for looking in your books. Otto Perry has shots of UP's plows, and some very interesting shots of a CB&Q plow operation between Cheyenne and Sterling with a flatcar-cum-plow. Presumably they would have borrowed from the C&S?
JAC