It sounds like the rebuilder may have screwed things up. The quick fix would find a passenger car carburetor that fits and came from a car with around 400 cu in. There were hundreds of those 409 Chevs hauling grain from the Texas panhandle to the gulf coast during the 60's. Most of the 409 guys just put another carburetor on them. I ran a GMC that was born with a 371 Olds in those days. I simply threw away the GMC/Holley with a governor and put an Olds Rochester on it and ran along with the 409s. As Jerry mentioned, get a tach and don't worry about a governor. My shift points were between 3800 and 4400. If you are not used to the old things, you probably never well get the revs up that high any way. They get pretty noisy.

If you find a carburetor off of a smaller engine, it will work fine. It may not have top end power, but you probably aren't going to be hauling 60,000 lbs of grain either. A carburetor from a smaller engine will give you better throttle response. One from a larger motor will give you a flat spot on acceleration a be more likely to back fire when it is cold.

I'm not sure exactly what carb your engine was born with. I have a book at home that covers the 80 series of the 80's. But I will be in Germany another week.