bilstein
Approximately 6 or 7 years ago I upgraded T-bars on my 71 340 duster. Big improvement in ride and handling. That was step one. Next thing was new bilstien shocks on all four corners. Another significant improvement. Probably the bigger of the two. Couldn't really believe the improvement. I did this in a two stage process so I could determine which items made the best improvement. Both were significant. After a number of close friends experienced a ride in the duster the question arose "what did you do ". Since then I have ordered a set for my 69 swinger, my 1997 3500 ram dully. All have given significant improvements. The close friends (5 at least) have all ordered bilsteins for they're rides. Mostly A bodies but a C body and a ram in the mix. All happy. So my take on what brand to purchase is definitely Bilstien's. I ordered mine from Firm Feel. They came with all the proper hardware and dust boots. Simple swap. My only regret is I wish I had done this years ago.
Good luck with your project.