If coolant is getting inrto your oil you'll soon need more than a head gasket. Usually coolant will bead up on the dipstick and is pretty obvious. A large amount, as you describe, should be easy to see. If it's getting into the cylin ders firing chamber there should be some sort of telltale exhaust coming out of your tailpipe. There's only so many places the coolant can go-on the ground, into the oil pan, into a cylinder or into the cab. If you don't smell it, or find it in the oil or see smoke then it is probably on the ground, Try parking over a fresh, clean piece of carboard and check for any leaks that way.