does the 10x1.25 tap match the existing bolt size and thread density?
Thanks.
If you have access to a MIG or ARC welder, weld a nut onto the part sticking out of the knuckle still and it'll come right out with a wrench...works every time.
I always use extractors as an absolute last ditch effort, usually becuase they break off and you're SNAFU'd from that point on...
At this point you've got two real choices, 1) torch the knuckle until that tab is a nice red and get on it with some vice grips and twist out the remainder of that bolt, or 2) MIG/ARC a nut back onto the remainder of that bolt, and make sure you pool some extra weld on it to get it good and hot, then go at it with a wrench.