The thing you need is the air powered die grinder with a big burr , but those aren't easy to find these days.
(Not the little HF one, the big 2 foot long & weighs 40 pounds one)
Angle grinder, even the big electric ones , just doesn't have the balls to push the kind of abrasive you need.
Masonary chop saw with a carbide masonary blade will cut it cross wise, but you have to figure out how to get it in there, and gawd help you if it twists while the (fragile) blade is in the cut...
If it will fit into a forge, hot cut is the way to go...
Used RR track is basically work hardened manganese steel, it is harder than all heck, and tougher than a 10 cent steak, rr's did not like their track wearing out all the time ;P