I have pontiac phoenix springs in the rear with the f body isolator so I can use an open spring on top. I have cut the springs and the isolater can move a little and put the spring out of position when the wheels are hanging with standard length shocks. With a pigtail that isn't a problem because they are flat but with an open spring it needs to be sitting properly...and yes a linear shock never changes compression or rebound rates. I'm curious to know why you want to run different compression and rebound rates. The HD adjusts according the road but no matter how fast it adjusts whatever it's adjusting for has already happened.