Dan, those 36" cars are probably the former Florence & Cripple Creek ("F&CC")cars bought and used by the Montana Southern RR in the teens and used into the late 20s. The MS also bought a couple of use F&CC lokies which are now long gone.
I was at Alder Gulch after the NNG Convention in Denver. Those ARE F&CC cars -- the initials are on the castings. One such car was rescued by Bob Richardson and helpers back around 1958 or 1959. Apparently, some CCC boys has found it up near the copper mill at the outer end of the line. hopped on, and released the hand brakes. Had a bit of a runaway until the car derailed on the grade and curves below the ghost town of Coolidge.
Also at Alder Gulch was the only known (allegedly) remaining gondola dump car of the F&CC. It's very different from anything seen on the D&RGW or the C&S. Used like a drop bottom gondola but very different approach to dumping.. Naturally, I photographed almost everything in sight.
I also wrote a story 2 years ago about the Montana Southern. It's posted as a PDF file in he files section of the RGS Yahoo! Group List along with some photos in the Photo Albums on that List's home site.
Hart Corbett
Novato, CA
F&CC Drop Bottom Gondola: