Blown head gasket?

[f00g00]

Minimum would be a gasket set for a head job which you can get from toyota
but I'd go a metal gasket for the head scince it has to come off and ARP head bolts scince they can be torqued more than the standard toyo ones, new plugs (iridiums), wires timing belt scince it also has to come off, new hoses for the rad, new heater hoses, check the plug on the back of the block,
if that goes your water goes out in a few seconds and the temp guage probably won't catch it,(no water or steam left to make the guage go up),
clean all your intake manifold parts including the ISV and while the manifold is apart check all the mating surfaces for warpage(TSRM shows you how to do this), clean the injectors, change oil and filter and again within a week cause of the water, flush and clean cooling system, clean the valves and piston tops and probably other stuff that I missed. The gasket set should have every gasket for the upper half of the engine and a water pump gasket. For sure change the injector seals which are also in the kit.
Its complicated and best left to pros who have Supra experience unless your a good mechanic yourself and have the time and the tools.