Those are not the common 73 / later A body brakes. Those have pins, may be B body, but I'm not familiar with changes over the years, nor am I familiar with brakes on E and other bodies. My 70RR calipers looked like those
Maybe to get the ball joints to fit they welded the outer parts of the arms you your original inner part of the arms.
The A body calipers are retained with a sheet metal clip and two small bolts on top of the caliper, not cross pins