See if he can also "index" the crank as he's regrinding it. That puts the throws exactly 90 degrees apart. We used to do that on round track cranks, even if it meant a good standard-diameter crank had to have the rod journals ground 10 under to get the indexing right. If your main bearing journals aren't worn out of round or scored, there's really nothing wrong with just polishing them instead of regrinding. That would give you a 10/20 shaft with just a bit of extra oil clearance on the main bearings.
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!