HELP rebuild my carter or buy new eddie ?????? 340

I would rebuild the AVS you have. They're easy to do, the kits are readily available, and they are for the most part very dependable. The 68 340 carb is a 625cfm, but if you are looking for bolt-on performance you can find the same carb for a 68 440. It's one of the oldest performance enhancements for the early 340's. The big block carb flows about 100 more cfm and will still bolt up with all of the existing linkage, etc..