Brake pedal spring

I'm presently putting a '70 challenger back together and need a little advice.
I have a spring that I had tagged " brake return spring " . This is an auto trans car.
I can't find an obvious place on the brake pedal arm to install a return spring.
Is the spring for the break pedal or is it for the emergency brake pedal ???

Your advice would certainly be appreciated.
Author: PECO