I only ask because I know of some locals who bought a HZ sedan with a 308 and factory air, they could never get to run cool enough and in the end sold it. That was from new. I have heard other people say it wasn’t unusual for similar problems.
To me it would be fixed by putting a radiator with more rows in it. But WB they did completely update the radiator and all the V8’s had a full shroud. To me that says Holden recognised there was a limit on the HQ to HZ radiator efficiency.
Just a thought.