I've got a Marlin Model 1895M Guide Gun in 450 Marlin. It has been used on 7 bison to date and only one took a second shot and that was only because the shooter tried a brain shot and was an inch high and just creased the skull. The second shot to the shoulder dumped the animal.
The 450 Marlin is basically identical to the hottest 45-70 loads so what can be said of it will hold true for the 45-70 as well. There hasn't been a bison born that will survive being hit with either in the vitals. That being said, bison can be a little tricky because the heavy thick hair can make things like a brain shot a little tricky. The shoulder shot kills them quickly and efficiently and is my shot of choice. As to recoil, the guide gun will kick since it is pretty light for a heavy caliber. It won't hurt you but it will let you know when you touch it off.