Tony said; "a bad idler or pitman arm should make the car dart to one side or the other"
That's right, Tony. The reason for this is, with a loose idler you car loses all control over factory toe specs. preferable toe-in is between 1/16th inch to 1/8th inch. With a bad idler, your toe can vary in and out as much as two inches.
Strut rod bushings effect caster angle. This too can be a problem but what we're talking here I believe is toe and the tire wear and handling problems the loss of toe creats... now. Upper and lower control arm bushing affect everything. Toe, caster, camber and the whole works. Early mustangs with the coils ontop of the upper a-arms were notorious for bad upper ball joints, bad control arm bushings, strut rod bushings, tie rod ends, Idler arms etc. etc... It's real easy to diagnose an early mustang's front end if you know a little bit about one. if it were me, I'd take it to one of my local front end shops, if I wasn't sure about it. They will probably give you a list of what's REALLY wrong for next to nothing.