Sorry I don't have a picture at the moment, but after many years of taking apart E-bodies I just noticed a new one.
Later 70 model years have a bracket with 2 studs sticking through the firewall where the clutch/brake support bracket attaches. This bracket is only visible if you take off the Drivers Side cowl screen.
Because of these studs, the Clutch/Brake Support bracket has 2 oval shaped holes in it.

I'm sure others have noticed this, but I just saw it.