Originally Posted by scarlson

If you don't care about the cups, and they are soft metal (you said anodized so I guess they're aluminum), why not just lightly file them down to near JIS? Forcing aluminum cups into a steel frame would also work, but be careful you don't deform the cup. The frame wins that fight because the aluminum is really soft metal compared to the steel frame, and we know the cups are pretty thin walled because they fit between the steerer and the headtube. Done properly, you'd probably just have a JIS headset at the end of the day.

It's not much you need to take off. Concentricity won't matter for such a small amount. Headsets are designed to take a bit of off-center if necessary..