Another approach would be to rotate the carbs a few degrees, plug the original stud holes, and drill and tap new mounting stud holes. No adapter required that way. It would be necessary to get a little creative with throttle linkage geometry, but it's all eye candy anyway. You'll still have one too many carburetors, no matter how you go about the project.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!