Rattling noise while driving

[legacy]

I just got a 1928 Model A with a multi disk clutch. I don't have any experience with a Model A.
I was driving the car and something started rattling, it got worse if I pushed in the clutch pedal.
I removed the inspection panel on top of the bell housing., there is a disk that is right ahead of the throw out bearing. That disk is loose and I can spin it on the shaft. That's what is causing the rattling.
What am I looking at here and what do I need to do to fix this.
Thanks