Many of the original GE designs used a double reduction gear unit with a parallel mounted traction motor. On standard and broad gauge, these were sized to fit between the wheels. For narrow gauge, the traction motor had to extend past the face of the wheel. GE claimed that the reason for the articulated design was to allow clearance and support for this traction motor arrangement in narrow gague, hence the 47 ton C+C version of the 44 ton (CATS15/19) and many B+B "Steel Mill Specials".
The standard GE 70 ton was designed to run on 60 pound rail, by making the narrow gauge version C+C the axle loading was kept low enough to run on 40 pound rail. The C+C narrow gauge was developed for Brazil's meter gauge in 1947 and uses the GE747/GA22 traction motor/gear unit combination with the motor mounted at right angles (like SP 1, SVRR 720) so did not have the same issues as before. The articulated design may have been adopted to allow better tracking, spread the wheelbase and allow sharper curves with a train.
The USP units were unique in that I think they were the only North American and 36" gauge units of this design - all the others are in South America. At the time USP ceased operations, there was little demand for an enigne of this type. BR&L may have held them for a while trying to find a potential buyer, but their only real value was to be salvaged as parts to keep other GEs running.
The C+C 70 tons have no major components in common with the USG 54 tons - they use different engines, main generators, traction motors, trucks, carbodies, cabs and frames.
It was my understanding that most if not all the usable narrow gauge rail equipment from Death Valley Railroad went to US Potash. I can't say as to what was actually used in New Mexico.
