Just because he said something about offset grinding the crank, doesn't mean the stroke will be any different. Just that they want to move the piston higher in the bore at TDC closer to zero deck.
If they are using original 318 rods they can't move it much, a 30 thou regrind usually means 15 thou off of stock "all the way around" I guess they could take most of the 30 off the underside of the crank throw, and little off the "top side" which wouldn't alter the stroke from oem.