Hex nuts removal
 

Been lucky so far with the exhaust studs but having some trouble with the hex nuts, whats the best way to remove these.

Heat them up to cherry red with a map gas torch. Let them cool and soak them with penetrant. Get a good grip with a a hex head wrench and hope they don't round off.

If they round off, you can use a dremel cut off wheel to split the nut and chisel it off carefully with out damaging the head stud.

Good luck.

PB Blaster applied over a couple of days along with some tapping with a small hammer to try and break the old corrosion. Used dremel on any really stubborn nuts.