The service manual doesn't give you many options here. For centering all it says is to load the machine with a normal load of laundry and a full load of water, let it agitate for three to four minutes, then stop it and check for proper centering. If off center then tighten the springs as necessary to bring it back into proper alignment. Once that's done repeat the process until the tub remains centered. I hope that helps.
By the way, the service manual is available at Automatic Ephemera if you don't already have it.
