A 4WD suspension is made up of quite a number of components designed to insulate the vehicle cabin (and hence the occupants) from the harshness of the surface you are travelling on, whilst still providing feedback to the driver to enable the correct response in braking, steering and handling.
The two main components of any suspension are the 'springs and shocks'. Essentially springs (coil or leaf), torsion bars and airbags are designed to hold and control the weight of the 4WD and are the true absorbers of shock. Without springs, you would not require shock absorbers (or dampeners), and you would feel every pebble on the road that the tyres came in contact with. Shock absorbers and struts or dampeners are really designed to arrest the bounce that occurs when the springs absorb the sudden movement of the wheels and tyres, thereby keeping the tyre in better contact with the road surface and providing improved safety, handling and braking.
Then there are many other components consisting of arms and rods with bushes (once again to absorb harshness), shackles, u-bolts, bushes, strengthening brackets, lengthening brackets for swaybars and brake bias valves, etc. These may or may not be needed for your suspension upgrade. We only list Ironman suspension kits on our site as their kit price is the same regardless of the spring rate in the kit.
It is really best to talk to Peter or Ben at Redlands 4WD to obtain a suspension that suits your needs. We don't work with terms like 'heavy duty' or 'extra heavy duty' - we will ask a lot of questions regarding the constant weight you have in addition to factory fitted items, as well as the occasional load and the use of the 4WD. We welcome and encourage you to contact us to discuss your suspension requirements.