Weird metal piece included with the new truetrac diff

If you have green bearings don't worry about it. If you have the tapered rollers put the slug in the center. Install the non adjustable axle. Slip the adjustable axle in so you can back off the adjuster and slowly snug it up without bending the retainer/adjuster base. You may have to back off the adjuster some more. Then adjust the bearing load per spec.