The .45/70 or .50 Aalskan should work just fine. I did one up in .45/70 many years ago and it was a super success.
: Loads used matched my .458 2" exactly as to velocities.
: We used 68gr. H335 with 350gr. Hornady's and 400gr. Barnes Spitzer bullets, both rifles giving identical velocities - 2,269fps with the 350's and 2,149fps with the 400's. A drop tube was necessary. Pressures were fairly low and becasue of that, the muzzle flash was fairly bright.
; Also, 66gr. 4320 worked fine with both bullets for almost identical velocities. I also used that load for 500gr.Hornady's in the .458 2" for 2,060fps.
: DON'T USE THESE LOADS IN ANY LEVER ACTION RIFLE!!!!!
; A .50 Alaskan with 500gr. Lyman cast bullets at about 1,850fps would make a good thumper. There may be some custom bullets available in that calibre.
; Harry McGowen, St., Anne Ill. makes very accurate .50 cal barrels in 24" twist which will handle bullet weights to 700gr. easily. I definitely would NOT get a 15" twist, which some barrel makers cut. That fast a twist is not necessary, except maybe for modern .50 cal. match bullets of 800gr. or heavier. Over twisting hunting bullets is not good for deep penetration. - in my most humble opinion, of course.