what springs are you running with the Mopar 528 cam?

The recommended spring, P5249847, 1.68 - 1.70 installed height, a single spring with damper @ 1.5 diameter, 2.07 thick wire of chrome silicon .480 - .535 lift range.

Those are the spec listed. Now you can do a cross ref on other brands. I did not see a rate in the catolog. They do provide rates in the engine book which I do not have on hand right now.