Rebuildable center link end? Didn't those cars would have that. Are you sure you didn't crank the end cap in too tight and bind up the socket?

Maybe back the cap off a notch or two and see what happens.

Edit, you should be able to visually check the preload on the center link end. Rock the steering wheel back and forth with the front tires on the ground. The stud should move slightly in the socket as the springs compress and take up the slack. No play indicates the springs are in coil bind and too tight. This could be exacerbated by a worn ball that isn't perfectly round anymore.