>From your description, I would vote for the Chrome plating and base layer(s) as the problem, too much where you do not want it anyway.
I would not be that excited to tap it out with my taps as chrome is tough. The narrow shell is not that big a surprise, I have seen many cut down, some from the factory, on one bike I had I had to face it down to 65+mm just to get a decent amount of land for the cups. The producer had just cranked the heck out of the shell during fabrication, deforming it. It was on a Bob Jackson in the mid 70's and it was unfortunately not an isolated incident.
When you do get cups to fit review the BB face dimensions to centerline, as your chainline may be unique.
John Jorgensen
Torrance Ca USA