'70 Duster front-end rebuild + steering box

Hey guys, my '70 Duster 318 has been a bit scary on the highway lately. It sways from side to side by itself, and I have to constantly correct the car (making sure not to overcorrect it or I might be in a bit of a pickle!). I tried playing around with the adjusting screw on my steering box and all it did was make the wheel feel a little bit tighter, but I still had that "mind of its own" behavior on the highway. Is this from my steering box, alignment, or possibly both? It will be a couple months before I will have the money to rebuild the suspension and get a new box, so I'm just trying to make sure that's the problem. What have been your guys' experiences with old, then rebuilt suspensions?