I think using a cone as first pass on one end and a relatively deep insert on the second pass on the other end will get things close enough for what we’re talking about needing done.
I feel I’m going slightly off-topic here a little as really I was commenting on the fact that if the faces of your bb shell aren’t perpendicular with the thread bore then when tightened, a bottom bracket that seats on the face of the shell, *may* have issues with binding and premature wear.
I’ve seen this many times when a bb is swapped out for a different type. I admire the analysis you’ve done but it doesn’t alter the fact that I’ve fixed binding bottom bracket spindles by chacing and facing the shell and I bet many other mechanics have too.