not sure why they can't be fitted to SLR suspension. My disco has been converted to springs with the air lift in side. the only reason i can see is that the SLR is softer suspension and the ACE will work harder on reducing the role. Saying that my disco was origanally on SLR suspension with standard ARB's when manufatured.
I've just removed the old ACE bars from the rear and fitted the new extreme bars last night. the fitting was very easy and so far I am very happy with it. next the front them I will be looking at upgrading the shocks