I'm interested in this as well as the rears on my 400 are too soft as it bottoms out with anything in the boot or two up. Free Length and diameter I can measure but not sure about the poundage.
I read somewhere that the poundage needs to be 75% on what's on the fronts. The new GAZ's I'm getting will have 720lbs front springs so it leaves me with trying to find out what the free length should be...