Abraham Lincoln: Vampire Hunter

Have you ever read any of the annotated Sherlock Holmes? This runs in the same vein. ;) I described AL:VH to a friend as less entertaining and more (deeply) interesting. I now want to know more about the real story of Lincoln. I want to dig into the spots where fact and Grahame-Smith's creations meld together. Is there a real Henry? Did Will really get accosted by a stranger? Gah! I don't have time for the obsession that I could have over this subject.