If you cant get it out by the methods mentioned above and you have to use heat you will be surprised how little local heat is needed, a good hot air gun should help. The alloy will expand at a greater rate that the steel plug, plus it will help soften any sealant that may be bonding the plug in place. They are designed to be tapered so the further you screw them in the tighter they get. Overtightening only leads to the case cracking around the thread and you always have oil leaks. When putting the plug back, a little sealant and moderate tension is all thats needed.