I am a fan of Diff gears instead of T-Case Gears. Drone and I agree to disagree
There are three things that you should do:
1. Buy a rebuild kit for each differential. If you are going to tear apart the differential, you might as well rebuild it so you won't have to dig into it again anytime soon.
2. You will need a set of "cans" to hold the spider gear pins in place. Many vendors sell them.
http://www.acksfaq.com/difcans.htm.
3. find a copy of the Samurai Factory Service Manual (FSM) to get the complete instructions with torque specs. I hear there's this cool place called Ack's FAQ where you can download a copy for free...
It will become obvious that the cost for either dif gears with rebuild kits or T-case gears will be almost the same - possibly in favor of the T-case method. Dif gears are a more labor-intensive mod.
The debate between the two mods often hinges on whether one prefers the torque load to be spread throughout the drivetrain (T-case swap) or the torque load being isolated at the differentials (Diff gear swap).
Those are the nominal facts. Think and choose, Grasshoppa...