If you call Barry Grant and give them your engine specs, they will tell you what carb they make that is suited to your engine. They can seem snobby, but when given the right info can be very helpful. I can tell you that they will not recommend the 750 for your 340. It's more suited for a 440. They are a touchy animal to get right, but when properly tweeked will flow extremely well. I agree with Chryco. A Holley is practically bullit-proof and easy to tweek. They give great performance. By the way Chryco, I just ordered a Holley HP Street 750!!!
Edelbrock can give some problems. Some folks like them, but mine has an off-idle stumble that I can't seem to adjust out. Edelbrock is a good medium price carb. Demons are pricey. Go for a Holley!! Just my
Matt B.