This bracket used on Abarth was a standard 124 spider bracket used with stiff suspension trailing rods.
The Corsa bracket was strengthened by welds on of additional material. We do not have a good 124 Abarth Corsa picture. (We are trying to obtain such photo and will post it as soon as we succeed).
In the meantime by comparison: picture of the same part from 131 Abarth Corsa shows very well how much and how this part was strengthened.
Here is the same 124 Abarth Corsa trailing arm bracket after weld-on strengthening :
The purpose of this strengthening is to protect the trailing arm and the bracket from being separated from the car floor by hitting a hard stationary object and gathering dirt. This strengthening also calls for appropriate strengthening of floor at the bolts inside the cockpit.