[Jeff Lee]

He is talking about the AFCO rear shackles. The rear leaf connects to the shackle with a roller bearing that slides fore / aft. The shackle assembly bolts to the rear frame and the spring can then move with the roller.
To answer the question, I believe you have full race weight and driver. Adjust so the slider is at mid-travel. I have not used so I can't offer any other advice.