I'm going to let it cool down now, then I'll top off the water and heat it up again before letting it sit overnight. Tomorrow I'll flush it really good multiple times before filling it with 50/50 ELC and distilled water.
Well @IDIBRONCO expressed concerns about possible issues if I left it overnight, so out of an abundance of caution I pulled the block drains and the lower radiator hose and poured two gallons of water down each of the heater hoses (and through the heater core). I poured two gallons through the radiator, then plugged the bottom of the radiator and filled it with water before pulling out the plug.
I was quite impressed with the crap in the drain pan!!!!
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I'm glad I flushed it!
I do need recommendations though. Do I need to fill it with water and heat it up again or do you think I've flushed enough of it out to just fill it with coolant? I plan on dropping in a new MOTORCRAFT thermostat just to be safe.
It's going to sit overnight with the block drains out and lower radiator hose off.