It's also possible to drill a hole in the bolt head and use a cutoff Allen wrench and a BFH to form a six-sided socket. Use a Vise Grip to hold the Allen wrench and form the hex with one hard blow. A 1/4" drill bit and the same size hex wrench should work about right. I'd suggest machining a close-fitting alignment shaft that fits the block and the oil pump mount to keep it in place while re-bolting it.
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
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