What is the point of your question? Are you going to model one of these lines? The size of the rail is what was there when the line moved from a revenue line to a tourist line, or what ever came available to build a new museum line. The size was not by any choice or reason of a special pick for a special weight of engine or equipment.
If Hesston needs more joint bars and plates for that 78# NYNH&H rail they might buy it from CAMA at Kent, CT. where they have much more than they can ever fit on their grounds. CAMA has given much small rail to WW&F and they came and truck it out, but WW&F will not use this larger rail, as it is not their historical size.