I would think it certainly would handle the .45/70 - as you make the pressure for THAT ctg.what you want it to be - for whatever action you use. The .45/70 was great for NA game with BP loads, and with smokeless is better yet. There is available a LOT of loading data with loads from the teens, say up to 19,000CUP as well as data from there to all the way up to 50,000CUP.

Firing pin size will have to be addressed if this action is to be suitable for higher pressure loads than about 28,000psi. the large pins of shotgun will handle pressures up to about that high, in my experience with my Sharps with the huge Black Powder firing pin - pretty much identical to shotgun pins.

In the .45/70 case in the lower ranges, say below about 34,000CUP, CUP and PSI are identical numbers. when pressures get up around 40,000 or higher, I believe I've seen it noted that there starts a spread in the #'s, thus 43,000CUP, as max in a Marlin lever-gun, is not 43,000PSI, but actually higher than 43,000PSI.