If I had a $400 tool to mill it, it surely would have been fun. Instead, I feel today like a neanderthal with a hammer...

I suspect, I need to mill only 0.1mm of it to make it fit right. Duh. Should I attempt that with a file if my local shops lack JIS milling tool?

In the worst case, if I screw up, I can always bring it in to re-mill it to ISO...