The trains that ran from Salida to Pueblo used engines and cabooses equipped with dual gauge couplers. There are photos in D&RG employees magazines and AFEs showing the installation of dual gauge couplers on the cabooses. Don't think you could consider the coal trains to be unit trains as coal was shipped in high side gons, drop bottom gons, and the ex-Crystal River cars. I have photos of the Crested Butte yards in 1917 and the trains are made up of a mixture of car types and even a few C&S cars for good measure.