[SoCal LS-L]

So I was driving along merrily, going about 55 and all of a sudden I notice my temp gauge go from normal to above red I freaked and pulled right over, and steam started to rise from the left side of the hood. Opened the hood, my reserve tank was boiling from the radiator venting.......and it did so for about 10 minutes. After I squeezed the upper hose to make sure the pressure had gone, I removed my cap to find the radiator almost full. So im like wtf..... either my thermostat didnt open.... or my water pump took a bleep right? So now im worried about my head gaskets..... if theyre toast.... I have to pull the engine to do them right? How hard is that for the SVX's? Im borrowing a block tester kit tomorrow to get the final verdict..... this is my only car so tomorrow is judgement day.