I might recall incorrectly, but I seem to recall that D&RGW looked into articulateds (new simple and compound) and articulated frames (a la K-37) with SG boilers and finally settled on K-37 (basically K-36 frames altered for C41 boilers) as the least expensive approach of all.
At the time, funds were tight and profits were wangled by deferring interest (Rio Grande to the Pacific). The money for equipment seems to be allocated to the SG sections of the line since bridge traffic seems to have been the main money maker.
Doug vV