I've followed this post, and after reading about how gunked up the inside of the block might be, you may have severe blockage in one of the water passages, that's preventing all of the air, and corrosion, to escape.
The gurgleing sound should be gone, after all the flushes, and your previous posts about the heater core itself.
If you've only removed one of the block drains, and not the other, you'll have a difficult time getting all of the corrosion out.
You need to start again, and focus on the drains being cleared.

98 Gen 2.5
05 Pontiac GTO
91 Corvette ZR-1
2011 Kia Sorento (wifey mobile)
Clarkdale, AZ