64 Dart Suspension Upgrades

Sounds like you're on the right track following the suggestions that have been made. Be sure to do the subframe connectors as those made the most noticable improvement in my cars. 1"+ torsion bars, heavier rear springs and all new suspension bushings (including the offset upper A arm bushings to get some decent caster) certainly helped mine but the subframe connectors made the cars feel like I was driving entirely different and improved cars. New quality shock absorbers, torque boxes, lower control arm stiffening plates and sway bars are a notable improvement too.