Things that make you go hmm..... Basically a 4160 square board 600 CFM, but it was developed specifically as a emission controlled replacement and it is discontinued, I.E.: no longer available through Holley.
Theoretically you could replace the base plate with another 600 CFM 4160 throttle body. However, you need to find out if that would actually work, based off of what other changes were made to the internal passages that routes the fuel to the Venturi.
At this point you are already having trouble with the carburetor, you might be better off just replacing it with an Edelbrock or another Holley. This really depends on what manifold you have. If it's a square bore manifold then it's going to be easier and less expensive to just stay with the square bore carburetor.
If you're using a spread bore manifold and an adapter, then it might be better just to go back to a Quadrajet, or the spread bore Holley. Then the other thing to look at is the future of your engine build. Are you wanting it to stay as it is now or are you wanting to improve it? So you would also might want to look at maybe going larger than a 600 CFM and going with the 650 or 750 CFM, yet that would have to be a decision you would have to make.