C20 and C10 Spring rates

[Nima]

Hi:
Are C10 springs and shocks softer than C20s? If yes, are they interchangeable? I have been reading a lot as to how to soften my 67 C20 without going through major expense. I read a lot about bags but since the springs on my truck seems to be stock ones, I thought changing them to a softer rating spring/shocks may be a good first step. My truck is stock height with trailing arm, spring, shock and leaf springs on the back. I also didn't want to swap the axles to C10 since I have already have 4 disc brakes and I kind of like my 8 lug wheels. My truck is not a work truck really.

Thanks,