400 headers @&^#

welcome to the wonderful world of old exhaust systems don't blame the car the trouble starts the day there started.I have seen them a lot worse than that at lest you have something to work with.heat is your answer get the nuts cherry red and get a good six point socket on an extension and a ratchet or get one of those new sockets made for rounded off nuts.be pashent curse softly and it will come off.......Or take every thing off and put headers on.good luck...........Artie