The rifle can get into Ruger/Modern rifle loads easily, it just depends on whose data you use, Hodgdon and Hornady set Ruger loads to 50kcup(kpsi), levergun at 40kpsi, and trapdoor at the SAAMI MAP of 28kpsi, others use lower pressure levels for each level, for instance a max Lyman 48th Ruger load is equal to a max Hodgdon or Hornady levergun load, also be aware that CUP and PSI have equal values in the 45-70, but you'll see most data as CUP. Best advice is start in the upper Trapdoor loads and work up to
your maximum, not the rifle's maximum, most folks find upper level 45-70 loads too much for them long before they reach the rifle's limit.
All H&R BC frames are SB2, they've never offered SB1 framed BCs or Handis, older H&R Inc(out of business in 1986) Shikaris had cast iron frames similar to SB1, were made before NEF/H&R1871 made SB1 or SB2 frames.
Tim