Phil,
+1 on the turbo timer.
Especially if you are out running the Z hard ya need to cool those bearings down. It's a cheap investment that will add life to that rebuilt Holset.
I am a Blitz guy have there gauges and timer, none are in my Z at the moment but I have used them in the past. I had this same one on my Shiro. It's small enough I could tuck it inside the ash tray out of site. It measured my coolant temp as well the timer. You can set it for 1,3,5 and 10 minutes. On my Shiro it would sense how hot the motor was and if I did a short trip to the store it would run for a minute and if I was out running it hard it would run for longer. It has a kill switch built in and a single wire ties into the e-brake. If the e-brake handle drops the motor dies.