New QA1 Spring replacement question--Spring Rate?

[HPCOBRA]

I have a Classic Roadster Cobra with a 460, cast Iron heads and a Richmond 5 speed. I recent bought a QA1 coil over conversion kit (ms3500). I had an issue with the short rods on the shocks, but fixed that by installing 2 inch extenders. The shocks now are close to the same travel and length of the stock shock. The springs I installed are 500 pound springs. I installed the spring on one side only. The car is resting on jack stands on the other. The suspension moved rather free with no spring installed so everything looks good. With the spring in, when I put a floor jack under the lower arm near the ball joint, the suspension only deflects about an inch when I pick up the one side. The springs are sitting on the spanner nut about .75 inches from the first thread. I can’t wind it down any farther because the locking nut hits the lip of the raised flange on the lower are that was originally used to located the factory coil spring. I took it all back apart and am going to remove some of that flange so that I can back the nut and spring rate off a little. Do these springs relax a little over time? Do they behave differently dynamically when driving , or do you think I have too heavy of a spring? Any help would be appreciated.. Thanks