Thanks for posting that link! … I've been remiss in not trying sooner to find more information about 3000/81/314 in response to Clutch's questions. The photos on the site you link to are about the best I have seen. The trucks look as if they might have the same general design approach as those on the MRS-1, but how similar they are in detail I don't know. I'm not sure where I first read that this unit was adjustable in gauge, and I have so far not found any details about how the adjustment could be made. (Was it ever, in fact, adjusted? It was tested on the 3-foot-gauge D&RGW lines, then operated on WP&Y, which has the same gauge, then went to Guatemala, where I think some of the railways built to serve the banana industry -- the name of the company that bought it translates, I think, as "Banana Development Company of Guatemala" -- so all of its actual service life may have been spent operating on the same gauge. According to Johnston -- see below -- the unit "saw yard service in both Durango and Alamosa… ran road service to Farmington and Alamosa, where she also served as a STD gauge switcher [and] even handled standard gauge trains (with idler car) to and from Antonito." So perhaps it was "adjusted" for standard gauge when switching in Alamosa, but it could have switched standard gauge cars with an idler car on dual-gauge track.)
I note that WP&Y acquired the locomotive in 1973. The tests on the D&RGW were in 1958, so the unit seems to have spent a fair bit of time in storage.
The February/March 2002 issue (vol. 4, no. 1) of "Light Iron Digest" has a short memoir by Roy E. Johnston, Jr., a test engineer (drafted from GE's locomotive division into the Army transportation corps) on the 1958 tests. The unit seems to have had at least as many … umm … "issues" as one would expect in an experimental prototype. Not much in the way of technical detail, but
-- it had an 800 hp Alco diesel engine (first iteration of 6-251 design?)
-- it was built for operation in cold climates -- "the Army needed a design that could be safely stored at 50 degrees below zero [and] have the ability to start and run within a reasonable time without external assistance"
-- the frame was built with special steel that "did not become brittle at extremely low temperatures […] structures above the platform were mostly aluminum, keeping the cg as low as possible."