What I’d do is balance the crank with whichever plate would suit the immediate need(auto or std).
Then modify the other plate(if possible) to duplicate the imbalance of the first one.
I shouldn’t be. The 5.9 Magnum is about four ounce-in. less offset than a 360 LA. So I think he is right, it’s a difference in manufactured parts here.
But then again, I have never run a balancer for testing any of this stuff. Just theory.