i took a look at a series III today at work (thanks linda!), and saw what i could see...
and assuming we're right about where it ends up on the lower intake, than it'* just some sort of a fresh air intake for the lower manifold. no idea why, but that'* what it is. on the new aluminum upper (series III), instead of making it'* way to the TB, it just shoots straight up to the top of the plenum, into a vacuum line, and then to the air intake tubing, just in front of the throttle body. Made a lot more sense that way than carrying over the series II design. If you get the chance to look at a series III tb, i do recommend it - it'* very slick. and small. it'* an electronic TB, so there'* no IAC, so they were able to package it just slightly larger than the diameter of the neck on the upper intake. very cool. and because of that, putting this passage through the TB would have made it more complicated (and expensive to make), as well as more complicated and expensive on the new upper intake.
so that'* what we've got. i'm pretty sure.