After another 4+ hours I managed to gain some ground:
When suction at the drain didn't work I tried air pressure followed by vacuum pressure at the top radiator vent. This loosened up the gunk enough to clear the drain. I then ran whatever distilled water I had through the system and -forced- it out the drain. By the last gallon the water coming out the drain was clear and ran freely. I filled the system with distilled water, ran the engine for a short while and then drained it out. I then filled the system with the recommended coolant, first filling at the radiator vent and then from the reservoir. Ran the engine for a short while and topped it off. I then took the Jeep for a quick test drive and the coolant level remained unchanged.
I'm not sure whether there really was green coolant or if what I was seeing was water + coolant + gunk. At any rate, I've run nothing but HOAT coolant through the system now twice.
Although I only took the Jeep for a quick test it seems to run cooler than before. The temp gauge used to go to 12 o'clock after about 10 minutes but now only goes to 10 o'clock. I'll give it a more thorough test tomorrow. I'm afraid the heater core is still plugged. It only blows warm air if I leave the vent selector to "recirculate", otherwise the air is only slightly warmer than outside.
At any rate, I'm relieved that I was able to get through this one before the temps drop below freezing. I think I'll probably do this one more time once the weather warms up.
Thanks everyone for your help, advice and suggestions.