Looking deeper, these discussions are from my Chilton manual. It looks like the carb stud is also used for the vacuum advance valve. Looking at the upper left picture, there is a fitting coming out of the carb that supplies the thermo vacuum switch (5/32 with red stripe). That same picture in the Firebird Parts Catalogue lists (1) a hose 5/32"x1", and (2) a tee fitting.

My solution will be to cut 1" of red stripe hose and place it between the vacuum fitting on the carb and the tee fitting. The red stripe hose going to the thermo vacuum switch connects to the other straight leg of the tee. The branch will then be the source of vacuum to the AC system.

If anyone with original vacuum advance, PB, and AC can confirm this arrangement it would be much appreciated.