If your bearings and king pins are ok. Check the play in the steering linkage with the wheels on the ground (with help) and make sure all drag link and tie rod ends are tight. Toe in or the lack thereof will also give you steering instability. Then last adjust the steering box. This is a very sensitive adjustment and will take you several tries to get it right.
Some years ago after doing many of the things mentioned above, I replaced the radius rod/wishbone socket. I believe that the old one was a poor quality repro. This really helped a lot.