I assume you installed the springs with the pigtails pointed in the right position??The pigtail on the rear springs need to be at the rear of the vehicle and pointed towards the left side of car(Both springs)The front control arms have 2 small holes in the bottom of them.The pigtail needs to cover one hole but leave the other hole clear(for drainage)If any of the springs are positioned incorrectly, that will affect the ride height on all corners.
Its highly unlikely, but if one of your strut/shock rods was seized in a certain position, that could cause the affected corner to sit higher/lower than the rest.You probably would have noticed while changing the springs though.If one of the sway bar end links is bent or tightened a lot more than the other side,it can cause a height difference between both sides.
A rusted out strut tower(at the upper spring perch) could also cause a leaning issue,but you would have noticed this when installing the new springs. If any of the control arm bushings are severely worn or binding up,it could keep that corner from settling all the way down like its supposed to do.I doubt this is your problem though.As SmurfStang alluded to,the car could have been wrecked before you bought it.The body or frame could be twisting(if you drive it hard at all)going back to the post accident specifications(highly unlikely if the problem just began)Frame/body twisting is something that would probably occur over time(mileage) vs just popping up out of the blue.If you jacked the front of the car completely off the ground then put blocks under the unibody,do the same thing to the rear of the car,then measure(each corner) from the unibody to the ground,this should tell you whether the frame/body is twisted.This would need to be done on a perfectly flat,asphalt or concrete surface.Doing the inspection this way takes the suspension components out of the equation and shows whether each corner is the same distance from the unibody & ground.If all 4 corners aren't close to the same height,the frame or body may be twisted.
D.S.S. 331 10.5:1
Trick Flow Top End
80mm maf/70mm tb
1 5/8" Longtubes
Cat Hpipe/2 Chamber FM