jetskibob1, the approximate spring rate you need can be calculated with a bit more information from you. You don't need to go get the car scaled, but I do need to know...
Spring free height=13"
Spring installed height= (exact height, don't guess)
Spring wire diameter= (measured with calipers to the nearest .001)
Spring coil diameter= (the diameter of the spring center to center)
Space between the spring seats at the desired ride height=
Distance between the shock mounts at the desired ride height=
When this information is known I can calculate what the rate is of the spring you currently have, and then knowing the installed height it can easily be determined what the current load is on the spring. Knowing the unsprung weight can be helpful, but with a light car and a live axle, I just assume it is really heavy in relation to the rest of the car and adjust accordingly. Since we also know that the spring you have is WAY too stiff, that gives us a starting point to adjust from.
Let me know if you have questions.