340 carb size?

get a holley 3310 750 and tune it. you won't regret it.
I ran carter afb, avs, and thermaquads on many motors over the years, they work great when tuned properly. but, they arn't as easy as a holley to setup. it took me 20 years to figure out that holley is the way to go. your 340 will respond well to a 750.