A street driven car needs heat and small carbs. Two 600 cfm carbs even with a progressive type linkage is way too much. A single 500 CFM on a 350 is just about right for 90% of driving, with a 600 as a nice choice when you want to kick it in the butt:

Size = (Engine CI x RPM) /3456 X Volumetric efficiancy

= (350 x 6000) / 3456 x .85

= 516 CFM TOTAL !!!!

Most engines without major mods wont have a VE (Volumetric Efficiency) much greater then 85 - 90%. Seldom will you be running at 6000 RPM. Choose your carbs accordingly - but a FI setup would be a better choice.