Sounds good to me. I built a .45/70 on a Siamese Mauser for a friend in Smithers - decades ago. What a wonderful rifle.
It used the same loads as my .458 (2") American, for exactly the same ballistics.

350gr. at 2,296fps
400gr. at 2,150fps
500gr. at 2,060fps

All with exactly the same load for each bullet weight, 68gr. H335 and CCI250 or Fed 215 primer. Both our chambers had a bit of freebore.
These loads were safe in our rifles, might not be in yours.