Choosing the right carb for my car (340 4-speed)

In my opinion a 600 cfm carb is not enough for that motor. I run a 750 on my 340 which is also not stock and it runs great. There is no stumble when I punch it and it pulls strong. If the 600 runds good go with it, but I feel that your are leaving some performace on the table with that small a carb! JMO