NEF/H&R will tell you that they can be loaded with levergun levels, but many here, myself included, have shot low Ruger loads on late model SB2 frames, but be warned, the recoil is severe even with mid to upper levergun loads!!
It depends on the source of the data, but 45-70 levergun data typically goes to 40kpsi and ruger data to 50kpsi, the Handi is chambered in .500S&W with data to 50kpsi which has similar case head size to the 45-70.
Tim