Update!!
Well........ran the car last night..........
Other than the still low but a lot more stable vacuum (wavering from 6-10 in/hg, averaging about 8 in/hg) and some slight smoke at idle/driving (hopefully attributed to excessive carbon build up), the car ran.
I actually got it on the road and railed on it pretty good. Felt a lot better than it had before, felt REALLY dang strong up in the 6000+ range, but I still feel like it's got more left.
Afterwards, I let the car cool and kept an eye on things. Idling at about 1000-1150 RPM, it's still only pulling 75-80 KPA on the map. I'd like to see that lower, but don't know how to get it there. Once the car had cooled down, I pulled plugs 1,3, and 4. All three had a pretty good shade of white, which is what I wanted. It's FINALLY burning lean, instead of getting all carbon fouled.
Noteworthy: I had closed loop enabled, but I also locked the LTerms and STerms to 128, so fueling corrections weren't happening.
Then last night someone on CZ28.com mentioned to me about checking to see if the IAC passage plugs were in place on the bottom of the manifold. That's something I'd never checked, and I bought the manifold without the lifter valley plate on it. So, on a hunch, I yanked the manifold again. Did it in under a half hour. Sadly, the plugs were in place, so my vacuum issue still seems unresolved. But, the good news is that those flat GM gaskets were holding up REALLY well. I had some oil residue in the runners still, but I'm not so sure it's completely fresh as it is just residual.
The car felt good, but it also was pretty sluggish down low. I can't tell if it's a vacuum issue, tuning (still needs a LOT which I hope helps), or just needs gears. I will say that on a hard 1-2 and 2-3 shift the car was making enough power to make the thing REALLY floaty on the stock 108K suspension. I mean REALLY floaty too. :devil:
Sooooo.......getting new gaskets today and putting it back together, and going from there tomorrow.