Somebody would have to convince me there was such a thing as a missile made to go through 40" of armorplate. The Iowa class ships were made to do battle with Terpitz and Musashi and Yamato and to survive hits from 18" guns. It just isn't obvious that there's any way to make a missile with the destructive power of a shell from one of Yamato's guns.
Other than that, there is 900' of room for phalanx guns on either side of an Iowa ship.