Can a 458 american be rechambered to 458 win mag safely? The rifle has a surplus mauser action.

Personnaly, I don't see why not. Just run a reamer through it and clean it up. You'll probably want to cut a new throat at the same time so that you won't get exessive pressure. Since you say it was a 458 American, there's got to be a block of some kind that you need to take out. The existing follower should still work. Some of the guys who do caliber conversions will probably see this and pipe in.

you may want to look at your barrel profile. Being that the chamber is longer, make sure your barrel profile has enough meat to make the new chamber safe.
Steve

or just run a 450 marlin reamer in it and call it good...

won't mess up your feeding

but, yes, you could do a winmag or lott on it