The axles on my 1976 C-120 Auto are shot.
Unless you come across an easier solution, you're going to have to open the case and pull the axles. If it was me and the keyway is the only issue, I would have new keyways cut 180* from the originals. I've done that before and just used straight 1/4" keys. Just don't cut them at 90* or you might lose where you need to have the second set screw.