Raiders Off Road 4x4 Club

Rocklobster Transfer Box
This is possibly the best modification you can do to Suzuki SJ. It involves stripping a 410 & 413 transfer box, swapping some of the parts, having some machined and welded, then put it back together. Sounds easy, well It’s not too bad really. There's a link at the bottom of this article, which gives very good instructions and diagrams.
You will need specialist equipment to cut and weld the gears.
This modification will give you a reported 4.16:1 gear ratio, and 88% reduction in low range. It gives you the opportunity to use more of your gears whilst trialing instead of having to thrash the motor, also giving the engine braking we lack in

Rear disc brake conversion
This photo shows Suzuki calliper used, but has now been changed to Rover 600 to utilize the handbrake.
All the parts you need to convert your rear drums to disc brakes are from the front axle.

Pro Comp E3000 Extended dampers,
Remanufactured damper mountings and 4 inch extended braided brake hoses