Another vote here for the Marlin Guide Gun in 45-70. I have an Alaskan CoPilot, a Marlin 1895 Guide Gun modified by Jim West of Wild West Guns. It is a takedown, and he is able to do quite a few other great mods. A little pricey, but they are real beauties.
You can peruse his site here:
www.wildwestguns.com