55.2-59 Rochester 1 Barrel Carb Question

[Robert Crandall]

I am using a single barrel Rochester carburetor on a 1958 GMC 270 engine in a 1950 GMC half ton panel truck. I have learned from experience and from forums that a feature of these carburetors is that they leak fuel onto the manifold as is shown in the 'before' photo. I just put another kit in it. This time I sanded the mating surfaces of the top cover to ensure flatness. The 'after' photo shows a film of fuel already starting to show, but above that joint. I also notice a hole on the upper left side of the air intake. I have another carburetor that does not have that hole.

What is this hole? I did not find where it opens. Could fuel exit from that hole? Could or should it be plugged? Thanks!