I enquired about this myself before getting the .450. Now I am broke so it will be a while.

Easily? From my enquiries, a .450. Re-chamber a .45/70 to .450 No2 NE. OK, a .500 NE is also doable.

Much harder is a .577 NE and I understood not every Ruger No. 1 will do fit it. As there were differences explanined on some board somewhere in the models or years of manufacture. Can't elaborate as I can remember.

The largest I also heard of was .600. Not a NE but a modification.