Two things: (1) if your stock carburetor is functioning well; and (2) you make no other changes, then a carburetor change through the existing manifold is going to be of little or no help.

If your carburetor is a typical Rochester B functioning poorly, then replacing it with a Carter would be a decent upgrade. However, the Carter will provide little (maybe a few percent) benefit over the stock carb IF the stock carb is functioning properly.

Those who experience large benefits from a carburetor change and no other changes simply a malfuncting carburetor with one that would function.

Jon.

Good carburetion is fuelish hot air
The most expensive carburetor is the wrong one you attempt to modify.
If you truly believe "one size fits all," try walking a mile in your spouse's shoes!
The Carburetor Shop