I'm sure H.S.S. don't have records for late HZ, but would still be worth asking Ben his opinion, he would give you some light on the ZT engine prefix. I know ZT came in after June 78, but I don't know which plants used that engine prefix first etc, or if was implemented as the QTs ran out. I have had more HZs with Q engine prefixes than Z, but that could just be luck of the draw.

In my opinion, there would be a slim chance it's got the original spare wheel winch cup, as these got removed, changed & the cable broke over the years. Being 79 model, it would've had the alloy wheels from factory, & these were changed early in life very often & the spare wheel winch cap was quite different to the one for standard wheels.

Back in the day, most people didn't know there was different cups for different wheels, I had a HZ with 8" mags, & when I saw the spare was a GR78 on a standard rim, (it was around 6 inches taller than the mag with the old style nylon belted, square shoulder tyres on it) I bought a widened steel rim & tyre for the spare. I remember it was harder to get the wheel on the winch, than the tonners or ute one I had, so half the time I drove it round with no spare. Also, when the winch cable broke, you just went to the wreckers for another one, not caring what it was originally off, too busy cruising & enjoying life to notice it wasn't the same!