Your picture is pretty dark for my old eyes. It appears the pivot bracket is still present at your rear red circle. It also appears the front cable is slack and looped around to keep it off the ground.

Based on memory: Originally, the cable from the front attached to the bottom hole of the pivot bar. The two rear cables would attach to the 2 holes towards the top of the pivot arm. The pivot arm acted as a torque multiplier on the rear cables. Without it, you couldn't get enough movement through the cables to completely lock the rear brakes.There may have been a short bracket that the front cable stuck through and the nut threaded on to the threads on the end of the cable for adjustment. That bracket would have pinned through the lower hole in the pivot arm. Its been a long time, and the only picture I have here representing the cable attachment is really poor, and I have no way of reproducing it onto the computer. In a service manual it should be located in the brake section, rear cable routing. Gene