Once the pump is off, use a thin cutoff wheel on an angle grinder to cut the head off the bolt, and install a short stud in the block so a nut can be used instead of a bolt when it's reinstalled. problem solved!
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!