The magnet grabs the forward pedal so likely that is the "plate" referred to here.
Edit:
There is a s/n break between early version forward pedal and later version forward pedal. (s/n 440290 change where the plate is not used, it appears). There was a "dtac" upgrade on my early 4300 but don't recall just why.. a tech came out and changed something to do with the magnet holding the pedal, and it has worked great since then (20 years ago).
Showing both later on left and earlier on right here..