I managed to get the yoke off, lots of heat and lots of grunting. I think penetrating oil is a waste of time, it really does not get into the threads and AvE did a video that pretty much proved that it doesn't help where threads are not exposed and thus don't get coated.
What do you guys think, should this plate be replaced? One goal with this repair job is to get my draft control working again. Since the yoke was so badly worn, I decided it was worth the effort to get this apart to make an inspection.