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...?