It's mostly for looks. There are a couple problems. One is that most of the adapters are open. That is that there is no dividing wall between each side of the intake, as there is in the manifold. This makes it behave more like an open plenum, which typically results in less low end torque. Another problem is that you're still limited by the 2 holes in the intake so the added potential of the 4v carburetor will not be realized.
There are adapters that do a better job of maintaining dual plane functionality but they are much more expensive and you still have only the 2 holes for airflow.
A better, but moderately more expensive solution is to find a 1956 ECZ-9425-A manifold. They usually sell for under $100 and have the older 4 barrel pattern. With an adapter for the modern 4 barrel and a little machine work that the average person can do at home, it makes a great budget manifold.
Lawrenceville, GA