Hy Stove, I would clean the rust off of the flywheel and the pressure plate. The thickness of the disc is not as critical as how deep the rivet heads are in the clutch material, 1/32" would be the minimum for reuse. When you lay the components on the flywheel you will see a gap between the flywheel surface and the pressure plate mount surface, that gap is how much clamp force the clutch will have, the smaller the gap the lighter the clamping force, and the shorter the time the clutch will last, hope that helps.
