I'm pretty reluctant to loosen all the head bolts at once- - - -too much chance of the head shifting in relation to the block and the gasket and maybe creating areas that won't re-seal. I'd recommend draining the coolant far enough that any open-bottom bolt holes won't create a gusher if the bolts are removed one at a time to apply anti-seize.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!