OK I am going to have to do some more research! I have wondered myself about those little round holes. I don't recall seeing a ball there in the Rochesters that I have taken apart. So here it is:
http://chevy.oldcarmanualproject.com/carb/51rochester/51rcm30c.html Now my GM Rochester manual does not show the check ball but instructs to shake the pump assembly to make sure the check valve is free. I also see further down in this article it talks about the three balls.
