what carb for 340

Keep in mind that picking a carb by "cfm" is totally related to wide open throttle results. For maximum power, a 340 built your way will love a 750/770 carb.....again for maximum power.

On the street, cruising around, the total cfm is irrelevant. As long as you chose a carb that's not built for racing only, and calibrated for street or street/strip use, it's really only your right foot that controls things with the primaries doing their job.........A big carb will flow the same with a little less throttle opening & and a small carb will require a little more throttle to do the same thing.

Has this engine been run on the street with pump gas before? Aside from the carb question, the 10.9/1 compression has me curious?.......Just wondering how much timing you can run with it.

A 750ish carb will not feel soft down low at all, as long as you can run some timing.