I would file an axle before I started filing the frame. Much easier with a grinder. You're not taking off much past the threads, so it doesn't make it that much weaker. Pull the frame out to 120 (not that much), and you're golden.
Disc hub would be good too, it's a japanese racing frame being ridden on the street in the US and it's the most common make at that, anybody who gets worked up over it should probably be getting more sunlight and vitamin C.