The EMD MRS-1 was designed to be 56 1/2, 60, 63 and 66 inch gauge - making it adaptable to most railroads using standard or one of the broad gauges. The width of the traction motors prevented it from being used for narrow gauge without changing axles and traction motors, and posssibly the truck design.

The truck frames were drilled and tapped to remount the brake rigging to match the gauge being used. The wheels were press fit in the usual manner. To change gauges, the wheels would be pressed off, and pressed back on to the desired gauge seated against the appropriate spacing collars (normal axle seat for standard gauge).

Evidently the Alcos built to the same spec were not cosidered MRS-1s by the military, but referred to as 120 ton. I presume they had the same arrangemet. I'm not sure if the Alco RSD-1s were multiple gauge but my guess is that they were.

The other multiple gauge engines were some of the Baldwin/Whitcomb RSTC4 models, with the 4700N being the only ng one (claimed to have been used as a gunnery target before it was scrapped). Then there was the GE six axle #3000 that later went to the White Pass, then to Gautemala and now scrapped.

The US military no longer considers the operation of foreign railroads strategic, I doubt they have any multiple gauge engines left.

Many of the GE 50/52 ton and Cat powered U-series changed gauges. The best example of this is SP #1 that was built with standard gague truck frames so it could be converted later. All the other known 50/52 ton units were built with narrow gauge truck frames only capable of 42", meter or 36", except for four for Venezuela built as 42" and soon chaged to standard due to a planned gauge change. I don't think any of these were truly considered multi-gauge units, just the design allowed it to be done without changing trucks or motors in many cases.