Yup, you're gonna need a new carrier. Now if you buy a full carrier locker (ie, ARB, Detroit) then that will take care of the carrier.
Used gears have a tendency to whine a little. Primarily cause they're not likely to be setup identically. But in a Jeep, as much ambient noise as we suffer from, who cares about a little gear whine.
As long as the gears are in good shape, I wouldn't worry about it. But you're not gonna get a warranty on the labor if you install used gears.
Oh! One more thing. The best way to accomplish this is just to buy the axles from a fellow with a 4 banger that's upgrading. The 4 banger has 4.10s stock. Then you can cannibalize your current axles for spares.