That's what I used. Diamond abrasive cutoff wheel. Cuts a very fine line. I used a drop of gel CA in the gap and once it's cured the rails can never touch. Hard to even see the repair. I had my brother hold a vacuum close to the cutoff wheel while I ran the grinder. I also ran a big magnet over the area to pick up any filings. j
But I have to ask:
Did you use the cut off wheel on the rail flange tips?
If so, how did you get the diameter down in there without cutting up the frog?