There are three types of traction aids currently available for the Samurai. What they basically do is make it so both rear tires turn at the same rate, so that way you have more traction. This is because the stock differential transfers power to which ever tire turns the easiest in order to make it go around corners. Basically they break down like this:
Mini-Spool - Cheap, but not the greatest on road. Locks both rear tires up all the time, like a welded diff.
Lockright Style - Not quite as cheap as the spool, but if setup properly a solid compromise. Will allow one tires to turn freely when not on the throttle, so it just takes some getting used to while on the road.
ARB - Has a switch to go from an open diff to a spool. The best of both worlds, but is the most expensive. But if you wheel with one, you won't want to go back.
There is a really good write-up over at
http://www.zukiworld.com/forum/technical-discussion-beginner-repair/merged-'lockers-the-best-but-most-'-and-'mini-spool-vs-locker-'/ with some good discussions.
If you want to go with the SPOA lift, which gives you 5" or so of lift, I recommend going with the Sky Manufacturing Stage 2 lift. If gives you everything you need, 1/2 of the High steer kit that makes driving still safe and the wrap-around spring mounts that help your rear axle from being destroyed by spring wrap. You will need to do some welding but it's a solid kit.
But going to 31" tires is a pretty big jump. You will need new gears in the T-Case or differentials to turn the larger tires and depending on your driving style you might start breaking axles.
Have you tried wheeling your rig stock? It might be that you just need some rocker guards and under-armor to protect the t-case.
