We mixed a cup of green with a cup of dex at work years ago when the dex was just coming out. The dex clumped up into funky coagulated fluffy crap that floated around. It looked like it would plug up a radiator in a hurry. I would just flush it and drain the block and use one or the other.
Travis..

70 GTX project, orig 440-4, 4 spd, track pack, FC7, stripper/street racer special.