Rick,
Not asking about spring rates. I have a fairly good idea as to what it should be. Please read my question again. I asked where the spring should be compressed to? There is another thread about springs unloading because the shock has more travel then the spring. As to my situation the angle is pretty much 0 degrees with the spring in front of the axle. Which will increase the lb's needed. I am maybe going to try and copy something I have found. I am running a Corvette C3 rear. The package they sell comes with 600 pound springs. Shocks would be QA1 dual adjustable.
I have a pic of a suspension at my page, yellow paint, red Wilwood.
http://www.summitracing.com/parts/HAL-DDR4855P/