rear spring sag

[Theslo1]

I'm trying to find the reason why my left rear corner sits lower than the right. Looking under the car the left spring is nearly flat and the right has some arch to it. the left shackle is pushed rearward like I'd expect if the spring was weighed down more than the right. My thought is the left has lost its strength. Is there any other reason for the springs to have a different arch? As far as I know they are stock springs from a 68 or 69 b-body, the man that gave me the car said he pulled the housing and springs from a satellite and stuck under my 69 coronet so he could roll it around. Also the interior is gutted, gas tank is out, only thing in the car is 440 engine transmission (727) drive shaft and a spare set of heads in the middle of the trunk, but the car sat funny before any of that was put in. On of my friends suggested that because that is the corner damaged from a collision (minor in my opinion only the quarter, tail panel and trunk floor extension show damage) it bent the frame down. I'll try to get pictures asap.

 

[Cranky]

Put a floor jack under the center of the rear end and jack it up off the ground and look at if the front end sits fairly level. Is the left front sitting really low once the rear tires are both off the ground?