The nut in the middle of the attached pic is the one that secures the pedal bracket to the firewall. The stud to which the nut is attached, moves around with the bracket. This has the effect of not fixing the bracket to the firewall and the bracket 'clunks' each time the clutch pedal is depressed. The other two nuts which secure the upper horizontal face of the bracket are tight.

I can tighten the nut in the pic which tells me the stud has some kind of flat backing on it which prevents it from rotating. So my question is, is the stud supposed to engage some kind of tab behind the bracket so that it can pull the bracket tight against the firewall when the nut is tightened ?

 

I checked this out further this afternoon. It turns out that the bracket to which that rear stud is attached has failed in 2 locations. That bracket looks like a complete PITA to remove, so there's going to be some creative engineering to remedy this problem.