I tested all of the individual lines and fittings with a hand pump brake bleeder with vacuum gauge. Everything under the plenum checked out, so I buttoned up the plenum and put the power plates back in with gaskets above and below. Turns out I didn't need the TB coolant bypass line, the power plates aren't drilled for the coolant passage so it completely eliminates coolant from the plenum and throttle body.
I wanted to check the vacuum pump operation before putting the coolant back in "just in case"
. It occurred to me I've never heard the thing run since I've owned the car. I checked voltage at the plug, no issues there. Pulled the pump and found it was locked up. I bought the car from family in FL, it had sat for years in an unconditioned garage so I'm guessing the humidity and lack of use is what did it in. Got a replacement and checked the time between pump runs and it's now holding for 40 seconds between pump cycles.