9/10 its a grinder job, but if you canot remove that section, and assuming you cannot get a dremmel or smaller tool in there, i'm afraid you will probably have to drop the exhaust system down more, or access from underside from a ramp... only other thing you could try doing is using plenty of Rost Off (leave to soak in for a few days, keep applying...) and then hammer a smaller socket on there to attempt to remove... Probably easier to drop the system so you can get to it easier, but you risk knackering more bolts! Good luck! Pete