Well, I'll tell ya, my guess is that this was done some time in the past by a large remanufacturer. I have seen pictures of this. Now for the case of whether or not the passages are too big, that will depend on the engine it's going on. Depends on how big the cam is. If they do turn out to be too big, do as cliff says.
On page 122 it talks about the Eldebrock Q-jets with idle bypass air of .099 to .110. It also says that these passages can be plugged with a small piece of aluminum and redrilled if necessary. If you have a mild motor with a lot of vacuum you may not need them. I guess you could just drill the installed plugs. You can start small and progress as necessary. I think the idea is to use the bypass air only if you need it.
