The term 'platelayer' was the name used in Britain for the men who laid and maintained the "plateways" that were primarily used for coal haulage in the early 19th century. "plateways" were built using L shaped rails and the vehicles that ran on them did not have flanged wheels. Eventually, around 1830, with the coming of heavier engines and wagons, plateways gave way to edged rails and flanged wheels. Plateways were less able to carry the increased weights, and the track was prone to wear. With the coming of the first railroad and then railways, the word "platelayer" continued to be used to describe those workers.
"Ganger" is a term used to describe the person who would be in charge of a "gang" of platelayers.
"Lengthman" would be a member of the gang of platelayers responsible for a length or stretch of track.