apologies for bringing back from the grave a year old thread!
masi61 , did you ever go through with this experiment? after acquiring a 93 quantum ii frameset, i was initially hoping to go through a similar project until i hit the same roadblock discussed here. i think i've honestly reread this thread about 20-odd times.
i recently called phil wood and they gave me the same information provided to you. before calling, i was really hoping they might have had a different answer than what you heard a year ago. just like you, i was told to face down my 76mm bb shell to 73mm and install a compatible crankset, most likely a mtb crank.
your logic on cup specs and bb specs make complete sense. did you proceed with the installation and how did it go?