I've seldom seen a carb so bad that a rebuild kit wouldn't fix it. Your 4300 is a good street carb, not popular as a performance piece but in good condition it will run as well as anything else and better than most. Changing to a Holley or other aftermarket setup can open a whole can of worms that won't be easily remedied across the Big Ditch without the resources available on this side. Unless you're an experienced, die-hard tinkerer, I'd advise a rebuild or a remanufactured stock carb.