I kin play the cordeen.
My dad was the trainmaster for a Railroad. I recall his story of why they call them "gandy dancers'. It ws because they would carry the long rail sections from a track wagon (called a "Speino" for unknown reasons). The track wagon came up the track to an area to be refit or new tracks laid. 6 guys would pull the track sections off with a tool like a big ice tong and a vise grip mix , then they would hoist the ties up onto their shoulders. They would walk with a deliberate gait that in between the ties. This was a "duck walk" so the men were originally called ganders. The term became "Gandy" as a corruption .
I looked at Wikipedia and it said that the name was also attributed to a manufacturing company named "GANDY" (although no record was available of such a company according to Wiki), also a leverage tool like a big crowbar was allegedly called a gandy. So there are several tales of the origin of the name. I will stick with my dads because it makes sense , Ive watched the gandies pull rail off the spino and carry it up a section to be replaced, they had the walk down pat. (I worked a summer on the spino as the guy who was responsible for "refluffing" the ballast with a tool that was on the side of the speino car and looked like a big conveyor belt with brushes attached. This would suck up the ballast and clean it and reset it in the areas where new track was to be laid.
The actual name was SPENO(named after the corp that originally made em) and a car of the whole unit looked something like this one. There were other cars for crew quarters and ballast storage and swing arms for weed spraying. When the whole thing was hooked togethre it looked like nothin youd ever see. Most bigger RRs had several, but my dads company, the REading, was a smaller company with maybe only two of these unit trains with Speno equipment