Well... it's official. Head gasket.Sounds like a cool project! I know you're not asking...But if the head gasket is actually bad the right thing to do is change it (or both in your best interest). Especially if this is going to be an actual "drift van," do it the right way and you won't be disappointed.
I know there's some bandaid fixes in a bottle to get you home...But sometimes those fixes show up later in the form of clogged coolant passages, heater core, or blocking some tubes in your new radiator causing other inefficiencies.
LS Time!!!!