I have them on my '87 491 coupe, in conjunction with new rubber bushings and Eibach Anti-roll-kit. They are amazing!
I agree with everything that Steve Wong says above.
Without question, I'd install them again.
Raised spindle, double adjustable, digressively valved KW V3s, Eibach anti-roll kit, Elephant rubber bushings, ERP 935 spherical tie rod ends, etc, all assembled and dialed-in by Jae Lee. Taut and confidence inspiring, yet compliant enough (with compression and rebound both set about 1/3 of the way up from full "soft") so as not to offend. It's magical. Impressive, considering the 50+ year old suspension design...
Jae Lee / Mirage did a similar setup on my '88 491 cab, but with Bilstein B6 all around. That system is also very good and although it's a bit apples / oranges (different vehicle with a different purpose), I assure you that the KW setup is not only a different ballgame, but a different sport altogether.
Any G body I build going forward will have KW V3s. I've spent time talking to the guys at Makellos Classics and they are huge fans too.