I finally got around to installing this distributor and with it hooked up to manifold vacuum, the idle was rock steady and so was the vacuum reading.

I installed it at 18 degrees per the instructions, and I got 14"hg vacuum reading at my normal N idle. Then I plugged in the vacuum line to the manifold source (per FBO's instructions) and then the vacuum jumped up to 16"hg but 200rpms higher than before. Once I readjusted the N idle rpms back down, I ended up gaining one hg of vacuum at the same idle rpms that I had previous to this swap (24 degrees of initial with my previous distributor w/o VA). So now I have 15" hg at my normal N idle rpms (previous 14") and I now show 32 degrees of timing, and I had to back down on the throttle plates around 1/4 turn.
I like this manifold vacuum setup because it cranks with 18 degrees of timing, then once the engine is idling the manifold pulls the timing up to 32 degrees at my normal N idle rpms. It did show leaner on my O2 gauge but that will be an easy fix.
The FBO distributor is setup with the proper can for manifold vacuum and it appears to work well.