Gary,
I think that Craig and Ellen have clearly described what you are facing. In my manuals and parts lists, that part is the "water flange." I see 3 bolts and one stud with a nut attaching it to the head, and two bolts from above attaching it to the thermostat cover. I've never tried it, but if you need to remove it you might as well attempt it the easy way first. Good luck.
Out of curiosity, why are you removing it? Cracked? If so, do you know why?
Mike Jacker