That's the key.
.45-70 (except, perhaps, for some of the high-velocity modern loads) is slow, but powerful -- like a strong shove, not a hammer blow. Standing, it's not a big deal at all, since your body flexes with the recoil. Sighting in from a bench, especially with a curved buttplate on a vintage buffalo or military rifle, is brutal.
For sighting in from a bench, I recommend some extra recoil protection, like those gel things that go under your shirt. Winter is a great time to do it, too, so you can wear thick clothes. But standing, regular .45-70 loads are fun to shoot. Just seat the butt against your shoulder, as you would properly do with any long gun.