Hmm that sounds pretty interesting , next time I manage to go to Barns & Noble I will take a look for them.
To be technical, Its Sir Richard Francis Burton, a Neanderthal, Herman Goering, an Alien, and a bunch of others in the first book
'To Your Scattered Bodies Go'. The second book
'The Fabulous Riverboat' has Mark Twain, a Viking, a prehistoric giant hominid, The Red Baron, King John Lackland, Cyrano De Bergerac and a bunch more. Both are part of the RiverWorld series. There was a whole lot of 'world' books in the 60's and 70's. Ringworld, Waterworld, River World, all different, just with world at the end. Ringworld series is better than the Riverworld series IMO.