The ball needs to be installed separately from the torque tube to figure out the number of gaskets needed to get the right tension on the ball. The service manual says that you need to assemble it without the seal in the cover and check if the ball can be moved by hand. If it's too tight, add a gasket and too loose, remove a gasket. That's why the gasket kit includes 4 or 5 gaskets for the ball cover. I think you'd have to remove the crosssmember on a '51 (mine has one anyway) to get the torque tube out of the way to do that adjustment.
