Sway bars
Another vote for Hellwig. I have one on my '69 Valiant. I had minor installation difficulty with the K-member brackets, but that was Chrysler's fault. The upper and lower halves of the K-frame had the holes stamped before they were welded together, and on mine they were slightly offset. I couldn't get a bolt through. Fixing that was quick, easy work with the grinder. Other than that foible, the installation was straightforward and simple. The quality is excellent.