Make sure the shifter is in neutral. Grab the second/high shaft close to the front of the top with vice grips, or use a brass drift and tap with a dead low hammer.
I first soaked the top in lacquer thinner, to degrease, then in rust sol. Then kroil.
Is this a unit that came out of a barn? Or fresh off a running vehicle?
I also open up the plug for the detents, and kroil.
The shafts can bind up if both are not in neutral.