Started working service bulletin for AST skin cracking issue. Since my plane is not completed and has not been flown proceeded to replace the HS-1222 ribs with the new design HS-1230 ribs. Removed the two AST sections from the stabiliator by removng the bolt securing the two pieces together and then removing the hinge pins for the respective sections. Removed the 10 LP4-3 rivets from each section at the HS-1222 ribs per step 4 of the SB. Had a difficult time punching out the center pin of the rivet on several of them without denting the skin surface. They were very well set. Attempted to remove the rivets per step 6 attaching the control horns. Was not happy with the result so going to my backup plan of replacing the HS-1220 control horns which I had ordered earlier in the week as a precaution.
