There are companies who can make a custom suspension for your vehicle. Consider how such as Caterham, Ginetta etc actually make their suspension (and any other car maker of course) they have to sit there, work out the sprung mass, unsprung mass and so on and design springs and dampers to work. Arrange a meeting with one/some of these suspension gurus and you could get yourself something made up. But what the effect to your bank balance... that's another matter

However, on the other hand there's the chance once you've worked out the desired spring and damper rate, there's already springs out there which exist which meet said specs already. The front shocks would most likely be the biggest issue, given that Omega dampers are an all in one affair, the damper unit itself isn't a separate cartridge. However, once again, looking at the talented chap in the Netherlands, he's gone and overcome this issue and made his own dampers, too. (with Land rover droplinks I recall!)
Steinmetz, Irmscher and others do make aftermarket suspension bits to fit, however. suggested 30mil front and 20mil at rear maximum drop, if memory serves. The rear is already pretty low, you see.
