Did some testing yesterday - did a cooling system pressure test, and the system held 16psi like a champ. No leaks at all. I pulled the plugs out to inspect them, all looked ok, no difference whatsoever. Pass. side floorboard also looked ok.
However, when i shined a flashlight down in the valley of the intake, through the injector rail and the plenum, a nice big pool of coolant could be seen (barely, but it was there). I doubt it came from anywhere else but the intake gasket. So for the time being, i think im gonna chalk this one up to bad intake manifold gaskets. Gasket set is about $18, and some new oil and a filter plus some fresh coolant after a thorough flush should do that motor good.