Reuse old pressure plate or buy new???

Even though I'm asking some questions myself about the A Body A 833- I've owned more Blue Ovals and Bow Ties than anything else. Manual Transmissions need upkeep.
Whether your clutch is slipping or shot the heck out- replace the Pressure Plate as well as the Clutch Disc... and have your flywheel resurfaced. If you don't; you increase the chance of clutch chatter. This by itself will make you crazy after pulling the trans and replacing two of the three components. The flywheel in some respects is similar to a brake rotor in the fact that it receives massive amounts of heat and will warp. Flywheel resurfacing does the same job as cutting the brake rotors- gives you a straight surface to start the next step.
Do this job once, you'll be glad you did.
tpg