A 750 with vacuum secondaries is not too big for a 350 if you're looking for max power. Heatwave touched on the most prevalent problem, excessive fuel pressure. You don't need more than 5 psi on ANY carburetor.

THIS AIN'T FUEL INJECTION GUYS. MORE FUEL PRESSURE DOES NOT EQUATE TO MORE POWER WITH A CARB. IT JUST MEANS INSURMOUNTABLE TUNING PROBLEMS UNTIL YOU GET THE PRESSURE UNDER CONTROL.

5 psi....5 psi....5 psi....5 psi....5 psi....5 psi....5 psi....5 psi