Air Ride Technologies makes a coil over bag setup for our cars. It's a little pricey but well worth the money. It's pretty much a direct bolt in for the front, except for the fact that you need to open up the front spring pocket. You can save a little cash and do the shock relocate thing but I highly recomend the coil overs if you can afford them. The rest of the system is pretty much universal. All you need is to make the brakets for the rear.
I've got the ShockWaves from Air Ride Tech on my wagon and love 'em. They are expensive (~$850 pair), but they sure are great. I highly recommend you go with the Ride Tech products. They really know their stuff and their service is A+.
We carry a system for the caprice/impala..
For everything(front/rear/air managment with 5 gallon tank 1/2"line 8 valves etc etc..)
you would spend 1900.00
Comes with a warrenty andtech support.
Air Ride offers a similar system and a shock wave application.
There is something out there if you look..
Long Live The Air Suspension..