wouldn't the fuel in the bowls vibrate with the bracket mounted to the engine? it seems to me like a replacement set of rubber isolaters would absorb a good amount of engine vibrations...
Well the engine is solid mounted to the frame.
Best way was of course how Honda did it...Insulators - carbs - rubber boots - Airbox.
Point is to provide some support to the carbs
Those rubber boots holding the carbs on the engine do not stop all the vibration.
Besides they are rock hard-most of them.
Why the manufacturers went from phenolic blocks isolating the carbs from the cylinder head HEAT to the rubber boots, was to solve the heat problem and the vibration problem. But the heat usually ruins the rubber boot.