From studying a few postings, an online searching, it looks as though the coolant bridge on the X25E V6 engine fitted to the Calibra and Cavalier is different from the one fitted to the Omega.
The Calibra one has an extra coolant temperature sensor which doubles as one of the banjo bolts holding it the front head, so it has three temperature sensors in all. The Omega one (which seems to be more readily available) has two coolant temperature sensors and each end of the coolant bridge is secured by standard banjo bolts.
Does anyone have the part number for the temperature sensor that doubles as the banjo bolt? Or maybe a kit containing the coolant bridge, one standard banjo bolt and one temperature sensor/banjo bolt.
Despite much online searching I've not found any reference to this temperature sensor/banjo bolt, which looks as though it'll be a difficult part to source.