I had the same problem with my Duster with all rears even a spool. A lot of unibody cars are not made correct. The front spring mounts on the cars are not spaced evenly from the front A-arms / ball joints. I needed to correct this before moving the springs in. What I did was took measurements and found that there was a 1/2 inc Difference.
I shimmed the right side back to correct this. I made an aluminum spacer and uses four longer bolts. and it corrected the problem. When I moved the springs in I followed the front spring eye holed in the mount for the new location.
Most a-bodies are off. I've noticed It can be seen with the naked eye after doing many for others. When you look up from under the car. You can see the difference in the large hole in the rear frame rail in front of the tab extended from the mount to the hole. Check it from side to side and see if there is a difference.
Most non performance cars had this problem especially /6's. The mopar bodies in white were perfect. also all cars with the extra supports for standard shift cars or sure grips from the factory. It was the way Chrysler used up the imperfect bodies.
My rear body and floor section of my car is from a /6 car . I can get pics of my Demon or my Duster on rotisaries if pics are needed for the location they are correct 340 cars and not off. But my Orange Duster is way off. 1/2 inch as I said. Next time its on the lift when I get it out of the Race trailer I will take pics so I have them loaded.
Did you ever watch the burnout contests at Carlilse and watch some of the cars cannot stay straight. The problem is the rear is not straight and makes the car want to spin around.
I found a pic of the Duster on the rotisary. Look at the tab on the bottom of the rail and the distance from the hole. this is a pic of the front spring mount mounting location. My car was 1/2 inch off from left side of car to the right side of car. I know you guys will be checking your cars now LOL.
