Re: thermostat or head gasket?
Greetings, I feel your pain, I just finished replacing the head gaskets on my ford taurus, and let me tell you, its not easy and it takes a LONG time.. I would say you probably have a blown gasket from what you are saying about the white smoke and overheating, mine did the same, and yes, passenger side of each head was blown.
Good Luck, sorry I couldn't help. :(