Probably the most reasonable ones to find are midget/sprite, and mgb, I have both types and have thought of the possibilitys, they have a variable venturi that adjusts mixture to airflow so too large isn't as much as a problem as with normal carbs---I saw thislink that lists some of them, the earlier ones used in the 50s and the first year or 2 in the 60s have cork seals to prevent leaks---probably not good choices, the ones used in AH3000 are larger (4bolt) and have a rubber that probably won't like modern gas for long and are more rare and $$ ---you would want to follow the mg manifold with a balance tube between them, the mg maniflod doesn't fit well to the A block and ex manifold
Here is alink with an incomplete chart of mgb and midget carbs -
http://www.teglerizer.com/mgstuff/SUcarbs.htm