I'm sure it broke just where the cast ribbing ends on the back. That piece vibrates so much the ribs should have been designed all the way to bolt hole. It's a good casting but you need to get it hot ...
After you weld it again bridge the gap on backside with slot from cutoff wheel about 3/4" on each side of weld insert 3/32 bronze rod segment and jb weld in place as vibration damper it's hillbil ...