1997 Acura RL head gasket

Im trying to do a headgasket job on this car. But ive ran into a problem. Trying to remove the nuts that hold together the exsaust manifold. On the flange part that holds together the the rest of the tail pipe. There are three bolts. On each flange.A total of 6 nuts. They are so seized.I ;ve only been able to remove three.I"Ve used a breaker bar but that is only stripping the nuts.I"ve tried a torch no success.I've tried impact wrench no go.I"Ve also tried special sockets to take out stripped nuts no go. Any more ideas or help. Also is it worth to do a head gasket job with a car with high mileage?200000miles.