Started in on re-furbing my K75 S yesterday, thought I would pretty it up a little for pics to apply for collector plates and got in a little deeper.  Pulled the forks off of the bike and found this:



   A progressive spring that does not look like the fieche ( if I got that right), so someone installed an aftermarket spring which is great if it is the right weight for me.  What little riding I got in before winter didn't leave me with any impressions, the back end was so bad that is all I thought about.  
   Do not see any markings on the springs, anyone know of a way to figure out the spring rate on these. RaceTech website says I need a 0.9 kg/mm spring and that the stock spring is 0.74 kg/mm

There's a good chance what you have is:
https://www.progressivesuspension.com/product/1465/fork-spring-kit