Hi turbotojo
Yea, I know what you mean - tho I'm in Europe...
I've got a daily driver 1983 240TD and I live a couple of kms down a very rough track. I haven't found the best solution yet although if you want a front end that will not bottom out, try fitting the springs used in the taxi/ambulance version if you can find 'em! Uncompressed they are slightly shorter than standard, but they are way stiffer - they just won't bottom out. But I removed them after a while cos they were just too stiff over the rough stuff!
You could also try changing the rubber pads at the top of the springs, from memory the thickest for the front give +22 mm and it is possible to add a home brewed spacer to gain a few more mill.
I'm less sure about the rear. If it's very harsh that'd be the spheres I think. I know that this forum feels that the springs should hold the weight of the car unassisted, but I dunno if that's really true. Might be. Anyway, the ride height is goverend by the sls not the springs.
Another useful way of gaining a few mill is to run 15" wheels/tyres...
Just my thoughts, not much solid info... good luck
Giles