Hey Cylinder heads guys- advice needed

The “spring rate” is the change in force over distance....... nothing more.

A particular spring will provide a given amount of force at a specific length.
How you arrive at that length does not matter.

If a spring has 150lbs of force at a length of 1.900”, and 350lbs of force at a length of 1.400”...... the “spring rate” is 400lbs/in.

Adding shims, different keepers, retainers, etc, does not change the spring rate.
The spring rate is designed into the spring.