I can't answer the barrel strength question as I don't know what steel they used then, modern centerfire rifle barrels are 4140 alloy, shotgun and rimfire are 1137. As for fitting, many members have stated they've fitted M158 barrels to modern frames just fine, others have stated that it would take a lot of work on the underlug to get it to fit including the one I had, there must have been considerably big tolerances in the old H&R Inc frames.
I've loaded my modern 30-30AI barrel to ~60kpsi with 125gr bullets with no problems, so maybe MSP's offer would be worth considering, I don't recollect(but that's not surprising anymore
) anyone working with an older barrel with higher pressures on an SB2 frame, maybe they'll chime in on it. You could always tie it to a tire and pull the trigger with a long string to proof it, but I'd hate to ruin a really nice barrel.
Tim