Hi Larry,
That was the second incarnation of the Tourist Railroad In Central City, after the 1969 line was abandoned.
This Central City and Black Hawk Line was built a couple of years after all of the older (1969) equipment was moved over to the Loop
The line that you are speaking of had Court Hammond and FLoyd Cothran as the principal investors. The Ashby's had nothing to do with the line that ran the 71.
When I worked there, we were told by the C&S that if we attempted to operate the 71 that they would scrap it on the spot. By the time that you saw it, the BN had absorbed the C&S and they had no such qualms.
Rick