Hi Fro,
I recently did a full suspension upgrade on my SLS D2a - (but I kept mine standard height). I went with new rear OE Contitech Air Springs (as I had a leak in one), front HD King Springs and Koni Heavy Track shocks alround.
This setup keeps the ride as LR intended - supple, with a superb ride with very secure handling. Koni's are expensive (around $950 for a set) but well worth it and can be adjusted to compensate for wear, then can be re-built. Ive had Koni's on 4 previous cars (not 4WD's) and they all outlasted the car!
So you could go with SLS spacers, Kings HD Raised front springs and Koni Heavy Track Shocks (they do a +50mm raised version for the D2). This setup would cost more than other options but would retain the lovely Disco ride and improve the handling significantly.
Good luck !

