The distortion has to do with misaligment of the magnents around the coil of the yoke. You'll have to fiddle with them to get the picture right but it's best to mark the original position of each one before you start turning them. Be carefull for the high voltage !!

If it's impossible to get the display right after fiddling with the magnets, then there's probably a small short somewhere in the wires of the coil that messes up the display. Then the only option is to replace the Yoke coil.