Caster Caster Caster. What 67cuda360 said. Get the max + caster you can, maybe 2 degrees without any other changes.
Before you change any hardware changes, double check the caster. This made the single biggest difference in my 73 Duster's straightline driving. Before I had it adjusted, I had 0 degrees, and the bu,p sterring was scary!
If that does not help, use moog offset upper control arm bushings, and get the max amount of caster you can. 3 degrees would be nice.