Kind of a side thought, something I've been thinking about recently:
The historicity of the Book of Mormon does not turn on whether Zarahemla was a real place, or if the events in Ammonihah actually happened, or if Captain Moroni used military technology centuries earlier than it should have been available. Really, the only question is whether or not Mormon and Moroni were real people. Mormon could have had all sorts of false beliefs about his people's mythical past, and the Book of Mormon would still be historical. If Mormon was a real person, he could have been a lousy historian and the miraculous transmission method from his day to ours would be just as miraculous.