As stated the springs pre 2005 were 6 leaf and probably the same set up as the Rover engined +4 4 seaters.
The post 2005 4 seater springs are 2 seater 4 leaf springs with more curve in the top leaf. Good idea in principle as it improves ride but weakens over time. The single leaf is unsupported on its initial compression and flattens on the 2nd leaf .
A special coil over shock absorber would be ideal as it would assist the top spring, improve ride height and be a simple fit.
The spring would not need to do more than assist the existing set up and could also improve ride.
