I've never seen pictures of this display, thanks for posting them.
This Rotary bears little resemblance to the South Park's Rotary, which evolved into C&S #99200. That Rotary was similar in size and design to the D&RG's OM, and I don't believe it was ever owned by the DL&G. I believe it was owned by the DSP&P, and was used in the famed snowplow trials of 1890, when it was compared to the Jull snowplow.
This Rotary does, however, bear a striking resemblance to the C&S's other Rotary, #99201, which was used on the C&S Standard Gauge for many years. When needed, #99201 was placed on narrow gauge trucks and was used several times on the line over Boreas Pass, through Breckenridge, to Leadville. It was then used for many years after the last remnant of the line (Leadville to Climax) was converted to Standard Gauge in 1943. In those days the Rotary was pushed by a single 600 Class 2-8-0. #99201 is currently on display across from the Colorado RR Museum in Golden.
I don't know if #99201 was ever owned by the DL&G. I don't think it was old enough, but I could be wrong. The C&S was formed in 1898, I would guess this Rotary was built sometime after that.