Good Afternoon,
I will start by saying I am not an electrics man. I only have bits and pieces of peripheral knowledge picked up along the way.
The diagram you posted of the A2 earth points is as far I am aware fairly comprehensive. I understand these earth points are points where a main earth wire is bolted to the chassis.
I quickly scanned the A2 wiring diagram and quickly found your references 179 & 279. For 179 I found.
View attachment 108393
I take it to mean this point is a weld like this
View attachment 108394
There's are dozens of these welds in the wiring harnesses and I not aware of information to their location. These welds can often be felt through the wiring harness wrap as a noticeable bump. All I can suggest is unwrap the protective tape and trace the earth wire from whatever bit of kit you are dealing with until you find the weld point.
Apologies if you are aware of all of this.
Andy