[dsraven]

heat the screw head with a torch, like the hotest torch you have or can borrow-oxy/acetylene would be great, so it heats the screw head fast but not the surrounding area and then leave it until the whole area is cold. then get a large flat screwdriver blade with no handle, just the blade part, and place that in the slot in the screw head. the alternative is a large flat screwdriver that you can plut a wrench on the shank or an adjustable wrench on the flart blade.hold that with a vice grip or the wrench if applicable and then hammer it a few times. don't smash it, just hammer it a few times. after a couple of hits put some torque on the bit with the vice grips or wrench and hit it again with the hammer as you try to turn it. it may have been locktited in place or installed with an impact screwdriver because the engine builder wouldn't want it to come out by itself and cause disaster. if that doesn't work try heating it again and use the same method asap while it's still hot. worse case scenario drill or grind the head off carefully. I have had some luck with welding a nut onto things like that but it is not easy to get a good weld when down inside a small nut bore