the first thing you want to do is stiffen up the chassis. subframe connectors are a good start, along with an export brace, monte carlo bar, and stringer to tie the subframe connectors to the outer rocker panel. the stiffer you get the chassis, the more effective later suspension modifications become.
after that you want better springs, with the 351w i suggest using either a 540lb rate or a 620lb rate spring on the front, and a 200lb rate spring on the rear. step up to a good quality set of shocks, i like the KYB gas adjust shocks for an inexpensive upgrade, do the shelby mod that relocates the upper control are pivot point, and invest in a pair of boxed lower control arms.
after that you want to go to adjustable strut rods, roller spring perches, boxed upper arms, and a spherical bearing for the lower arm.
in the rear you want some form of traction bar, its hard to beat the shelby under ride traction bars or cal tracs.