Frank:
The 1923 D&RGW roster lists the stock yard at Antonito as having a stock capacity of 32 standard gauge cars and 40 narrow gauge cars and a sheep capacity of 16 standard gauge and 20 narrow gauge cars. This might have changed in the later years, I have no later data.
During most of the year, the standard gauge cars would most likely be moved out of Antonito by narrow gauge engines with dual gauge idler cars. During the fall stock rush, the Grande would sometimes run stock specials on the Antonito and Creede branches. I have seen photos in the 50s of a stock special on the Antonito line that was all standard gauge powered by a 4-unit FT set.