[Bill Cuthbertso]

I really think that there is no really correct position for the third hole. I think that the upper area is a convenient place to put the hole because there is alot of room.
If you turn carburetor upsike down and watch the butterflies open, you will see that the progression holes are not opened in sequence. All three are open to the vacume at the same time so I do not think it matters to much if at all. The size of the hole certainly does matter. 12 o'clock seemed to work for me, but I think 2 o'clock will also work. I used 12 because it was easy to eyeball that location from carb to carb.
Lets hear your thoughts.