Vacuum advance Drill'n tap manifold

So I'm thinking of drilling and tapping my lynx single side draft manifold to install a small nipple that can be hooked up to my vacuum advance. What size diameter should the pipe be and whereabouts on the manifold would it best be tapped? thanks

yeah, I searched a bit more on the subject and from what I can gather, the vacuum advance works in reverse if hooked up into the manifold. It's meant to tap into the carb before the manifold.
It seems that recurving the dizzy will be the best way to go. Not cheap though. Anyone in Bris who's familiar with this sort of thing?