Chris:
Two of the 490s were equipped with dual gauge couplers for switching at Salida. A few more had dual gauge coupler pockets, but according to the D&RGW records only two were so equippped. Two of the 480s were equipped with dual gauge couplers for the same reason (I have the data on that, but not handy...will put it here later). The D&RGW normally had two standard gauge switchers at Salida equipped for dual gauge switching. There were two C48s for a long time and diesels later. They equipped two of the 480s and later the 490s so that they could switch standard gauge gons at the barrel transfer in the event the standard gauge engines were not available. The Grande had a variety of C class engines equipped this was in the early days up to the late 20s, the the coal trains from Crested Butte and the rock trains from Monarch had become too long to be switched by a C class.
John Maxwell did drawings of the dual gauge idler cars and I have D&RGW original folios. These are the ones built in the late 30s, but there were dual gauge idlers before these that were wooden car bodies. The Grande used dual gauge ilders at Alamosa on the line to Antonito and up to Hooper and in the yard at Monarch. They did not use idler flats at Salida as they always had engines equipped for this.
The D&RGW also equipped some standard gauge cabooses with dual gauge couplers for use on the dual gauge between Salida and Leadville. The D&RGW did not have any idler flats at Leadville, but probably had dual gauge couplers on some of the C class. The D&RGW had dual gauge couplers on a few standard gauge engines and kept them on until 1940 as they took C&S narrow gauge cars to the smelter at Leadville which had dual gauge track until 1940. The standard gauge 2-8-0 at the Colorado RR Museum was the Leadville switcher in the late 30s and early 40s and it was equipped with dual gauge couplers for switching C&S narrow gauge cars.
Hope this is of some use. You might check the Colorado RR Museum to see if they still stock the Maxwell drawings and I know his family setup a web site for ordering copies of his photos. I do not know if they offer drawings, but I would be surprised if they did not.
