The stock suspension is pretty hard to improve on. The design was good enough that GM used it with only minor changes all the way up to '91 on pickups, and '95 on the vans. Improvements like disk brakes and power steering can be done without changing the balance of the suspenion system. The rear suspenion system is also very good, good enough that Nascar uses it under all the vehicles used in the top 3 series.
