What is this bracket?

[old Chevy guy]

I saw that happen in the 80's once. A buddy of ours had a Chevelle station wagon he had been given by his parents. In typical 16 year old fashion when the back brake line rusted out he crimped it off at the broken part so the car could still have front brakes. As he was leaving another friends house this day some of us taunted him to punch it and smoke it up. It was kind of a joke being a wagon and all as well as kind of a pile in general, but with a big smile he floored it and the motor mount broke of maybe was already broken and that old 350 stood up on its side and pinned the gas pedal to the floor. Totally caught off guard he slammed the brake to stop it but having no back brakes the car immediately started smoking the tires instead of stopping. Turns out that wagon had a posi and layed out about 200 feet of rubber and would have wound up in the woods but he got he senses together and just shut it off. We were all shocked and speechless. Luckily no one was hurt and we could laugh about it after. I can still remember the look on his face as his mouth hung open in terror. Priceless!