Thanks Dr Dlex - you're on to something!
The hitachi dcp-306 on the subaru is somewhat different than the dch-340 on the isuzu. The slow-jet is inside the air-horn/throat and not accessible w/o removing the choke/air-horn chamber. Nevertheless, there were 2 air bleeds I could spray with carb cleaner: the primary main air bleed jet and an adjacent hole which appears to be another air bleed - maybe for the slow jet.
Anyway, squirting either of these forced cleaner out the other as well as out the primary venturi nozzle (so they're all connected).....and, and......it can now idle again at a low rpm. The venturi nozzle is dry at idle (as I think it should be) but at higher rpm (open throttle) the venturi nozzle is now mostly passively spraying gas but still dripping somewhat, although not nearly as badly as before. Maybe I just dislodged some dirt/obstruction a bit.
I'll next try removing the idle mixture screw and the anti-dieseling solenoid so I can spray and/or apply vacuum to all the primary passages and see if that clears any dirt. I'm assuming that the venturi nozzle should never drip (only spray) under all rpm/throttle openings. Is this right?
thanks!