Dave,
I do suggest the 45/120 -- the cost is tiny more than a 45/70, and you can load to the same velocities as any safe 45/70, and be at far lower pressure.

if you are feeling up to it, the case is about the same capacity as the 450 NE.. within 3-5 grains of case.. and norma 120 brass is larger than knyock BERDAN primed 450 NE