Not TBs, but we did an original Honda Civic in the old days using a pair of SUs from a 1275 Sprite on welded up manifold to replace the downdraft original, which was fairly horrid. Gained about 8 mph in top speed.
I think that a bunch of any improvement you get in using motorcycle cars on a car engine is really due to the better flowing more direct shot intake manifold you have to create to do it