Drilling the butterflies was/is a trick the Holley guys would use if they had a hot cam and they had to raise the idle. The butterflies wound sometimes be exposing the transition slot(I guest similar to the needle jets) and screw up the A/F. With the hole drilled in, they can/could close the butterflies, get enough air in to keep the idle up and not expose that slot. I don't know how much "hotter" the 813 cam is over stock, but this is very interesting and a great idea.
Glad it's working for you.
