There should be no need for a new rear carrier since the lunchbox locker was simply inserted inside it after the OE spider & side gears were removed. Remove the lunchbox locker & insert new spider & side gears into the existing carrier. No setup is needed for those particular gears.
If you keep the OE carrier & simply put the shims back where they came from, keep track of which shim came out of which side, you will not have to set the back lash again.
You can often find used good condition side & spider gears with their required cross pin in a 4x4 shop that installs lunchbox lockers.