So back to comparison between the Exedy Stage 1 Pressure plate (pt no.:H22513) vs the Exedy OEM HD Pressure plate (part no.:FJC521).
Below is Exedy Stage 1 Pressure Plate (Pt no.:H22513) ---- note the centre springs which are different from the Exedy HD.
Below is the Exedy HD Pressure Plate (Pt no.:FJC521):
Below is the Exedy Stage 1 Organic Heavy Duty Clutch Plate --- note that there are more marked grooves, two more centre springs and the rivets are brass:
Below is the Exedy OEM replacement HD Clutch Plate: