Hi.
First you got to use the right springs for your application, we have been testing a few and ironman were by the worst on the kzj. I ended up with a mix of Eibach +40mm real, medium up front and kingspring medium +70mm at the rear which are actually a good +5cm no more. For long expedition, over a month in Mauritania with a lot of fuel, water, tools for the team and standard traveling stuff i added a 30mm home poly spacer on top of the rear spring to level the toy, great setup either empty and loaded. Eibach medium rear were way too low and soft.
I use slightly modified bilstein shocks(euro specs) up front which are the normally matched for rear landrover defender. The valving was perfect and they have a very long shock travel while keeping the same compressed length as the original toyotqa shocks. 2 mods to be done, the top fixing point, you need a bushing and 2 small spacers for the adaptation, at the bottom , just enlarge slightly the stud hole in the axle tab. You will have a 12mm lower rods which is a great improvement over the factory toyota 10mm one. Driving arround unloaded remove the front sway bar, it handles much better and offroad you will flex great even with light load on the axle (nose uphill situation for example). when heavily loaded on long trip i was putting it back on since the extra weight made the bar flex better.
For the rear, i used Koni shocks, serie 84, also for land rover and range rover rear. they use to be designed in the 80's for the landrover/rangerover used on the dakar. They were great, not too hard, long travel and not loosing efficiency, when heating up while being beaten in desert tracks. They don't exist anymore, i got one of the last sets available, but the serie 82 is very similar and should do about as good. Dont take the serie 90, they are way too hard.
I tested factory landrover shocks in the back (full hydrau), they were great around and on slow tracks, but after 1h african track they were way too soft due to the temperature, when cooled down they were back to normal. If you only do low speed tracks, no problem. The only mods needed are a 20mm spacer at the rear top bump stop and re drill of the axle tab for the 12mm rod.
I also tested euro specs bilstein for land/range rover rear( same as i had on the front axle), but they were too soft on tracks and not good enough in rebound on slow offroad, going up rocky steps for example.
Tested OME L series for lj/kzj, good for local offroad, totally useless for expedition loaded and their 10mm lower rod is just looking to let you down on a small jump or on a big twist. (had one to go on a twist and others leaked after 30mn african tracks, replaced under warranty and handed to a friend who use his kzj locally only). the OME L serie (long travel) were a touch shorter than the landrover shocks.
OME springs, not installed on mine but on the rig of friend were doing almost as good as my mix.
landrover defender / rangerover, rear shocks will increase your wheel travel by a bit more than 100mm front and rear, this is a huge improvement. You can't really do anything better without completely modifying the suspension geometry and going 3 or 5 longitudinal links.
I was using the same tire size as you but on BFG km1, 265 75r16, great size for a kzj used everywhere.
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