Just be aware that the limited slip & selectable lockers generally don't come with a ring & pinion, you are expected to transfer the ones you have, so you're going to have to start by finding a good used diff - yes it would be a good idea to fit new bearings & seals whilst you're in there, especially if you're not familiar with the unit you're dealing with.
Something else to be aware of is that ring & pinion gears are matched sets and should not be separated - you can't use a pinion from one diff and a ring from another, even if they are identical units, also setting up the rear end gears after bearing replacement is a task that requires specialist tools, knowledge and experience.
One last thing - if I'm not mistaken the Samurai front & rear diffs are interchangeable, front diffs are generally less worn than rear, so bear that in mind when shopping for used parts.
