Question for suspension gurus

The new tires will definatly help, however, being a mustang it is always going to understeer.
Modifying the mustang suspension is difficult though, because the rear suspension is designed poorly, and likes to induce snap oversteer, and suspension bind which creats bad oversteer. Not cool when you are taking a hard right hander.
What you can do is go with fresh struts/shocks all the way around. Something high performance would be good. You should definatly upgrade to 11" 5.0 brakes. They use different struts from your current brakes, so I would do them at the same time as you do the struts.
Then, I would go with stiffer springs. They won't help that much in ultimate grip, but they will allow you to make quick direction changes and
will make the car more responcive. If you are serious about it, get coil overs. They absolutly kick ass. CC plates will probably become nescicary to run enough negative camber and should really come early on.
I hear the sub frame connectors really help, but check the class you run in first. I beleive they are illegal until you get to street prepared, which is very competitve.
Beyond that, Polyurethane bushings in the front helps.
For the rear, don't put any bushings in the rear control arms. I wouldn't do anything with the rear control arms. Start with a pan hard bar, and eventually go to a torque arm if you get serious.
Thats about everything I can still out right now. If you have any more questions, just ask. If you are wondering where I picked all this info up, it was mostly from the "Mustang performance handbook 2" and www.cornercarvers.com or net, or something (great site to research, but are close nit, and arn't receptive to newbies).

I agree with getting subs put on, just make sure that you use full length and that they are welded in place. Mine made a huge difference and I would say to anyone else get them. You might want to try a Strut Tower Brace, that would help to tighten up the front a little. Since you have a 89 you can use a 4 point G load brace to help too.

Dan