Big problem, 70 L34 Nova

[Bavss70]

I have an 402 engine that is ready to paint but I neglected to remove a plug for the TCS sending unit on the passenger side cylinder head. The plug has a recess for a 3/8" drive. I have tried a breaker bar drive on it, tried using a cold chisel to drive it and it is starting to look a little worn.
Does anyone with their repertoire of experience, had any luck in getting a plug out of a 30 plus year old head?
I am worried about trying an acetylene torch as perhaps the head would crack. If I drill it out, I may lose the water pump.
Some how, some way that plug is going to come out before we have to tear off the heads, etc. and go to a machine shop.
Many thanks in advance, John.