I figured out to well what I am going to do. I am using
http://puppetswar.com/product.php?id_product=173 Iron Mutant heads for all of my Marines. Well it turns out they fit nicely into the hole for the Obliterator. They also fit nicely into the hole for the Terminator heads. They fit to nicely to not use them in all of my Terminators and Obliterators. So its time to tear off heads and get those minis looking cool.
Thus is the curse of true modelers.