Heck it may be snapped off. Will bend first to seize up and then breaks. Odds are the threads almost always bend or deform slightly right at the hole edge since force is applied there. Meaning most will not simply screw out when bent and then broken. Be d-mn odd if it screwed right out.
I'd pull bottom steel pan and then, using like a strong small Maglite, look up in either the last slot or the big hole in the bottom of the girdle, you may well see the pin and its' condition, if broke off then you can try to fish out the piece with magnet and maybe save yanking the aluminum girdle. Hope you like oil in your hair, it'll be like Brylcream in the '60s! If you found the broken piece I'd simply leave the broken pin remaining in the hole and tighten it to not leak. Make sure it clears the crank swing if you can see in there. Could save a bunch'a work. if you have to pull girdle, don't pull crank pulley, or damper, or timing stuff, or oil pump, I think you can do it without doing that. The oil pump pickup tube will have to unbolt but you'll see that.
Brylcream, a little dab'll do yah, Brycream the girls're gonna luv ya....................................