Nitride is for wear protection--who cares? Grind it using professional crank shop and keep rolling--if it was in a dirt car that was going to eat abbrasive all season yea nitride is a good thing but your engine will never know you cut through that crust--it won't care at all!!!! It will LOVE the fact that you now have round/true/untapered journals and an even fatter radius.
I have cut about 65 440 cranks down to 383 mains and raced the SNOT out of them--Never ever an issue----Grind it--race it--Forget it! It will not wear unless it had dirt in there so .......