I really like this idea. Perfect way to get the back face back square to the crank. Now I just need to spend some time figuring out how to mount it all. Thanks for the great suggestion.
But then suddenly, I realize there may be an even better way. Instead of a powered grinder mounted at the end of an arm, I think I could use a number of fixed cutting edges, mounted around the periphery of a well-balanced cutting assembly. Then I'd use the crank itself to rotate the entire cutting assembly, by simply putting gasoline into the motor and firing it up. At the end of the day, I get to say I have the only engine in the world that machined itself.
