The Rochester 1 barrel carburetor (B, BC, or BV) can use either 1 or 2 check balls.
This particular carburetor only uses 1 check ball. There is only 1 hole in the pump well (A). This is the discharge hole. Gas is fed by running over the rib (B) into the well.
Some 1 barrel’s require 2 check balls. These will have 2 holes at the bottom of the well. 1 for fuel entry and 1 for discharging. This type will use an aluminum check ball inside and in the bottom of the well.
The main discharge is (C). This is where the fuel discharges when the accelerator pump is pushed down, accelerating.
Also, at the main discharge (C), the bigger steal check ball sits at the bottom of the hole. The spring and T go above it.