any JZ series stat fits..
I don't think it's your thermostat, because the OEM stats failsafe into the open position making it impossible to overheat. Probably the waterpump if it's factory, the plastic gear lives to spin on the shaft. It's quite common.
Or could be bad rad hoses, clogged radiator (especially if your using the 20yo stocker), or just a BHG. BHG isn't as rare as you'd think on a *jzgte.