Okay I have been looking for this book for years now. It could be from 1999 to 2004. It is the story of two boys who are friends. They travel back in time as famous male friends such as President Lincoln and General Grant, and Marc Antony and Caesar. I think the book had a light purple cover with a picture of them. They tried to stop the deaths of the men but realized they couldn't. I also remember John Wilkes Booth in a tent. Maybe they were after a criminal and they had to catch him and he showed up as Booth and whoever betrayed Marc Antony.