Woohoo - looks like my instinct was correct.
From "Mr. F.E." himself, Mose Nowland, here is the answer:
Balancer hubs are castings of ductile iron for some high performance applications. DUC cast into the hub casting assures that it is the right material.If you have not heard of Mose, here is something to bring you up to speed:
Just one more reason for me to take him out to breakfast, lunch, or dinner to thank him.
While we are at it, any similar questions out there that you want me to bring up?