How crazy are you looking to get? The weakest part of the entire package are the torsion bars in my opinion. I've got a Fifth Avenue that I pretty much did everything to and still wasn't very happy with it until I put new bars in it.
Cop sway bars, frame ties, and modifying the power steering pump will give you the biggest improvement (providing everything else is straight) for the least amount on money spent. If you really want to make it handle:
-FF 300# torsion bars
-FF aluminum K frame biscuits
-Cop 1 1/8" front sway bar (civy is only 1 1/16") with poly bushings
-Cop 3/4" rear bar with poly bushings
-5 leaf rear springs
-Dump the ISO setup in the rear and run B-body shock plates
-Bilstein shocks on all four corners
-11/16" tie rods
-Modify the stock power steering pump regulator valve to turn down the pressure
This is what I did to my Fifth and it handles like it's on rails now.
'87 Fifth Avenue: 512 low deck roller / 518 / 8.75