I only know the front Sirion springs are 30 N/mm, the rears you would need to calculate.
To find the spring rate you just need a few measurements, length, diameter, rod diameter, and number of coils, then you just enter them into the spring rate calculator at https://www.thespringstore.com/spring-rate-calculator.html
To calculate the desired spring rate you just need corner weight minus unsprung weight, and the frequency you want. There is a pretty easy formula here on the forums Understanding spring rates
No need to over think it, there’s only a few values needed to calculate what you want, it’s not voodoo or magic. Just do the math and you will have a Good base to start making other adjustments.