My old SN95 car I did the Griggs GR40 Super Street setup (with a few upgrades to the kit). Awesome night and day setup over a modified 4 link (I had the Eibach Pro Street system and swaybars before the Griggs setup).
When I built my Cobra, I decided not to swap the rear GR40 stuff over and go IRS instead. I did the Full Tilt Boogie FT5000 kit and a FRPP Diff cover. Im on single adjustable Koni's and coilovers all around. All I have to say is, I love it! I'd never want or put back a solid axle even if Im making a 1000+ HP.
Also check out this article from Maximum Motorsports.