Here's two MC actuating arms (late and early with mech. brake light switch)
The loop on the left fits onto the brake pedal arm.
The opposite end fits into the back end of the master cylinder and actuates the MC spool valve.
Notice the threaded parts; loosen lock nut, then rotate to either lengthen or shorten to adjust the pedal height/threshold of brake actuation.
On early cars with a mechanical brake light switch (second image), the large disc contacts the switch arm to close the circuit to the brake light circuit.
In your attempts to adjust the brake pedal for more convenient heel and toe operations or ???, be careful not to adjust the engagement point too low. In an emergency, you don't want to run out of space and bottom out on the floor.
(borrowed images)
Sherwood