Are you sure you have a pair? Sounds like you might have gotten two rear carbs. The vacuum port is on the bottom of the front carb (at least for the TR3 version), somewhat easy to miss.
Anyway, if you use manifold vacuum, you'll want some way to block it off at idle. A friend of mine did that with Webers, by setting up a microswitch triggered by the throttle linkage and a vacuum solenoid from some emissions setup. He reported that it worked well, and lowered fuel consumption by about 10% (compared to no advance). I don't recall where he got his solenoid, but the wife's 89 Dodge Caravan with 2.5L turbo had one that would work, I think. Ditto for Dad's 73 Buick Estate with 455.