sukivel,
If the frame can handle 45-70 then 44 mag shouldn’t be a problem. Have fun.
About 10 years ago I gave away a NEF Pardner 12ga because it wouldn’t even sell for $50. I kick myself for that. Hadn’t got into gunsmithing for myself so I didn’t have a use for it.
One of the things I don’t like about these single shot shotguns, especially in 12ga, is the recoil. Making them into pistol caliber carbines takes care of that which makes them fun to shoot.