The back of a Unimog is better being sat down for stability, you guys concentrate to much on spring flex what you need to keep in mind is flex with your chassis this keeps the centre of gravity as low as possible Unimogs have very good clearance already keeping COG down should be your main goal.
Keep an eye on how you mount things to your chassis always three point mount, never drill holes or weld your chassis especially the front half.
Soft springs are great but you must keep an I on two things one is the angle of the u joint in the torque tube don't let the axle drop to far from the chassis this can be controlled by the shock absorbers as the factory do, but you want max travel and fit longer shocks, so you can fit a shock cord from the diff centre to the centre of chassis. The other is your bump stops keep them don't lose them and ideally the hydraulic ones are best.
Moose