if you've got the budget for it i'd go with the TCP coilover front and G-bar rear, the shocks are matched and can be had in single or double adjustable versions. get a set of subframe connectors as well, that will help the car feel more like a modern car. now if you only plan to do the front suspension check out the Global West coilover system with the "negative roll' version. i've heard that GW is also working on a new coilover type rear suspension as well right now, but haven't heard exactly what yet, so you might consider contacting them to see how far out they are on it.
if you just want to tighten the car up some and don't have a huge budget there's alway Opentracker stuff, he can set you up with whatever you need.
also don't forget that a raack and pinion conversion goes a long way to better road feel as well, for that you have a few choices, TCP, RRS, Randall's Rack, Steeroids and Unisteer. if you go with TCP stuff then use the TCP rack, a more budget friendly rack kit would be Randalls, Steeroids or Unisteer, stay away from the flaming POS Flaming River rack kit....it blows hard.
i also wouldn't cut the car up for a mustang II style system either