To me, the best thing you can do is repair the leak or have it repaired. If you change to a newer more modern carb (would need an adaptor to bolt it on), you start a chain reaction of things needed. In '56 the carbs had a unique and lower vacuum signal to the distributor diaphragm for spark advance. A max of about 4" of vacuum go to the distributor diaphragm. It's a combination of venturi vacuum and ported manifold vacuum. The distributors have no centrifugal advance and all advance is dependent on the signal from the carb. A later carb would involve swapping out the distributor also for a '57 through '64 Y-Block distributor to get proper spark advance.
If interested, I can help you with your carburetor leak issue. Assume it's leaking at the large round brass cap on top or the O-rings between the bowl and base for the fuel supply.
Sal