It may be covered in the thread referenced, but, stick a little valve grinding compound or even a paste made of ajax cleanser on the bit to insure a tight fit in the bolt. (make sure the cavity on the bolt is clean). Then apply force with a suitable tool to snap that bolt out. Worst case and you strip the bolt
you can take the arm off and either drill it out or get one from a junk engine.
I have done about 10 or 12 of these and haven't buggered one yet (most recently two weeks ago) It's scary when the bolt pops free- but yours probably will too.