The center bolt is not half way from front to back, it is 31" from one end and 25" from the other end. Yours does seem to have a lot of tilt to it, even with the shims installed the rubber at the front isn't even close to the spring. It looks like the bottom of the arc of the spring is about a foot in front of the center bolt. Do you have the weight of the car on the springs or on the jack? I wonder what your pinion angle is?
Big chief is correct about the so-called replacement springs. One supplier has two for stock height. A 115 spring rate with a 6-1/2" arc and a 125 spring rate with a 7-1/8" arc. With the same 575 pounds per sied on the springs the second spring will position the rear of the car 1-1/4" higher than the first spring.
