Jason, there could be a third option regarding the origin of this tender.
Sometime in the mid 80's, I was amazed to see an old tender set out from a Southbound freight on the old spur to IBM. It was right past the switch, next to the Diagonal, and had been set out because of a pulled drawbar. I pulled over and went over for a closer look. It had been used in non revenue service for a long time, but was definitely from the CB&Q family. Part of the number was still barely legible on the rear of the tank, and when I checked it out at home later, I found that it was a refugee from the Fort Worth and Denver, the other CB&Q subsidiary. This may well be it, as it was configured the same way with the oil bunker, and had just the same shape and size.
That's what I'd bet on as the origin of that tender, and if it is, I'm glad it survived.