I Got a couple of empty cases and played with them on my sporter and it does not look possible. The rim is the same size as the bolt channel. The rim can get all the way to the bolt with no modifications, but the  front of the magazine will be a problem and MUCH metal will need to be removed to get the opening into the bolt channel to feed. There may be no modification that will even make this work and I could see ruining a pile of receivers finding this out (this would be sacrilege around here). So unless you find one already done and that could be copied I would find another way to go.
Recommend you buy a couple of cases and play with them to verify my opinion.
I have heard of Japanese Arisakas and Siamese Mausers modified to fire 45/70 from the magazine. I think I would research them instead.
Using my son's NEF on pigs with 300 grain flat point bullets was a pleasant experience. Shooting them at night using a spot light you really hear the bullet connect and they went right down.