ALCO was only active from the early or mid 1950's through 1963. They were both primary contractors (responsible for an overall plant design and its operation) and secondary contractors (providing components to be used in plants designed by others.) They had contracts with the US Navy's program, I believe through Westinghouse (who was one of the only three primary contractors in the commercial sector for the USN program) but cannot confirm that they did not do subcontracting for either General Electric or Combustion Engineering.
ALCO Products was prime contractor on the US Army's "portable" plant at Fort Belvoir, VA. which achieved criticality in 1957. This was the plant designated SM-1. They also acted as prime contractors on the uprated version of this plant for Alaska (SM-1A) and for a smaller plant destined to be used in Greenland.
None of these was a large plant, in relative terms. All were designed to be constructed in pieces, and shipped to site in trucks or airplanes or both. (SL-1, which ALCO didn't get the contract for, was entirely truck-transportable to site location.) All were boiling water reactors.
My point is simply that, YES, I do know something about it, and that if any company were, at the time, in a top position to have experience with small reactors, it would have been ALCO or else Combustion Engineering --- but then again, with ALCO's in-house railroading experience, they'd have gotten the nod for any application of atomic power (as it was called back then) in locomotives.
Pure folly, by the way. What would have hurt them would have been the likelihood of application of a boiling water reactor to such a platform, which would have resulted in not only very difficult control problems, but likely very high radiation leakage to the environment (neutrons being the worst offender.) Pressurized water is a much more controllable design, but there again you would have had enormous problems with weight.
(This is exactly why the Air Force chose not to go with plans for atomic-powered bombers that used turbine-driven propellers, but rather went with a plan to use a reactor to heat air and thrust it rearward -- no cooling medium such as water or liquid metal was needed. The project still was calculated as overweight, and further design refinement resulted in ever-increasing weights, until the now-unworkable project was dropped.)
Some of this may seem irrelevant at first to railroad locomotives, but in my opinion on second read will be DIRECTLY relavant to the topic at hand.