With that kind of miles I would want to ensure that the top end is in good shape. Have you been able to confirm if it's just the head gasket or if it's more serious ie. cracked block or head? You will more than likely want to change the valve guides and seals as well as all the the seals such as the front timing chain cover, valve cover gasket etc. It would be a good time to change the timing chain given the number of miles. I'm betting that the head gasket has been replaced at least once before. Do you have any service records or history to ascertain if any work has been done before? As others have said, you do not want to be driving the car in it's present state.