Wow! This thread is about 2 years old. Just put new leaf springs on the rear. The standard eye will give you a factory level look, and the reverse or mid eye will lower the rear. Since your butt is sagging, you need to raise the rear, not lower it.

 

ya, i used the search. I know this is an issue with the old stangs, so i figured it wouldn't be hard to find.

 

The way things were originally, the springs set the ride height and the shocks dampen the reaction of the suspension to bumps and pot holes. Modern gas filled shocks provide some spring effect and can affect ride height, which means they are supporting some of the weight of the car. The shock mounts were not designed for this so.... ask someone who has used air shock to adjust the height of the car about damage to the shock mounting area.

So the short answer is replace the springs to restore ride height, replace the shocks if yours are bad or you want to alter the suspension performance.

 

if youre wanting to keep a semi stock look but level, run 620's and standard eye.I have 620's with 4 1/2 leaf mid eyes out back and i had to cut part of a coil off the front to get the thing level because they naturally want to sit back. But it looks nice and sits down on the tires just gotta be careful over continual bumpy roads cuz it touches the tires a bit.