Instead of Webers, why not try to obtain some SKs, which I am told are
Japanese/US copies of the Weber/Dellorto design.
I have seen photos of their SK47s fitted to a Triumph Vitesse and they take
all the Weber jets/emulsion tubes & air correctors.
They have their own pump jets & chokes.
SK make also their own trumpets.
These Carbs are supposed to flow as well, if not better than the Weber 48bs
I have no further knowledge of these carbs or where they may be found, but
perhaps someone can track them down on the web?
Hope that is helpful
Leon F Guyot