Which case is the 50 Alaskan based on, the 45-70 or the 348 Winchester? If on the 45-70, you would probably be ok, if on the 348 Win, then I would begin to be suspect of the cased head diameter and resulting thrusts loads and such. I know there is a firm that converts Marlins to both the 450 and the 50 Alaskan which is suggestive of the strength parameters required of these cartridges. This info is somewhat dated; Shooting Times, April 2003 but they show the three Cor Bon loadings which operate from 26,800 psi, to 49,500 psi. So if NEF is willing to go to 50,000 psi on that case head diameter (
?) so long as you were observant of pressures, I see no reason why you couldn't. Glad it's your shoulder though. I would be cautious of a cartridge based on the 348 Winchester case though, It is truely hughe at nearly 5/8" diameter.
As a side note, it strikes me funny that of the three loads shown, one is driving a 400 grain bullet ot 1676 fps and another is driving a 440 grain bullet to 1625 fps. The one load is solid in 45-70 territory and the other is at the far ragged edge of it. This cartridge does make a lot more sense in a rifle than in a handgun though.