Is it possible to remove a bung rusted solid in a cylinder head?Not until my old red motor was reassembled did I realise the replacement has a bung in it(passenger side to rear between manifold and rocker cover).I want to fit temperature sender.Otherwise sacrifice having a heater plugged in at front.What makes it so difficult is that it plugs into a water jacket.Probably been in for years.I've tapped it,heated it with propane and used a long socket handle and now is partly rounded.Obviously if it doesn't come out cleanly that could be the end of the head.Anyone have suggestions?

Mig weld a long round bar onto it at least 8 mm in diameter. Use plenty of heat and be quick to undo while theres plenty of heat. Done a few this way and never failed.

I would drill through it with an 1/8 cobalt Sutton drill new one, then use I barrel ball die grinder burr down the hole, keep going around with the burr eventually u will break through to the thread most times it will the collapses then wind out, other wise keep going with the die grinder burr till most of the plug is gone then clean up the original thread in the head, as a mechanic I have removed a fare few of others handy work like this.
if your not keen ring around local work shops as most have mobile thread repair guys they use as it a bit of art work to remover broken bolts, studs etc in situ.
when you start removing studs from like Nissan 6 in alloy heads then you have to be real carful the stud crystallise and go rock hard and the burrs and drills will go through alloy like a hot knife through butter, you can do a lot of damage real quick, good luck pete.