There are companies out there that will make the springs to your spec, find out the corner weights, top and bottom size and height you want, they will do the rest. Cutting springs isnt too bad on smaller cars but I dare say on a disco its not a good idea, I can see them falling out quite easy!!
I understand totally why you want be toying with this idea, a lowered disco will be a head turner and it pushes the modified boundries a bit which is also good. A few years back I see a series LR which was about 1" off the floor, it looked crazy but oh so good, I will try and drag a pic out soon...