If it were me in your position and I was doing up a C-body or an older Fury, I'd just go to FirmFeel and buy front and rear sway bars, Bilstein shocks, no smaller than 1.12" T-bars, Stage 3 PS box, and a suspension rebuild kit. I'd redo the brakes and install 17" wheels with a good modern tire on it. Heck, the C-bodies have so much room and such a tall tire, you may be able to get away with a modern SUV tire. Does Dr Diff have C-body brake kits front and rear? It doesn't need to be crazy. I'd imagine the 11.75" rotors would do, but a 13" kit with the Cobra calipers up front should help stop the big boy down a lot easier.