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...I have a set of piloted BB taps, and I know how to use them. I would still try an old school cup and cone bottom bracket as my first fix and see how it works. One of the reasons cup and cone went on for so long as the standard setup for bicycle BB's is exactly this...they tolerate misalignment better than a lot of other bearing arrangements.
If you can get the thing working this way, removing whatever metal shavings from the BB shell that will be produced by retapping it is money you could have spent on a different crank that works. You might get away with it, because a sealed unit BB bearing assembly probably doesn't require as much support for the thread cups that lock it in place, which is why they can make them out of plastic. But if it were me, even though I have the taps, I'd try the cup and cone route first.
Just in case you haven't worked on a BB with both sides Rh threaded before, the fixed cup needs to be torqued in there pretty tight. I usually use some blue Loctite as well on the fixed side, because I've had at least one back out on me in use. Which is annoying.