suspension upgrades?

is there any kind of suspension upgrade kit or components available for a 74 duster?, as my son is working through upgrading this basically stock Gold Duster, the 40 year old suspension just doesn't help the car through corners at all, now I know these never cornered good even when new but what are people using? urethane bushings, springs, or?, budget is a concern so air ride isn't going to happen here..ideas...?

You have been given good advise so far, but you are wrong about ONE thing. Compared to other cars from there time period, Mopars handled perfectly fine, there is NO inherent design problems with the torsion bar suspension. Keep it simple, rebuild what you have, upgrade torsion bar sizes and sway bars as mentioned....WAY cheeper than those aftermarket systems...