Sorry to hear of Murray's passing. We had some great conversations over the past few years since I have been a member. Always enjoyed his posts on the various topics. Condolences to his family and friends. Rest easy my friend.
Generally tires should be changed out at 6 around years, so at 12 years of age, they are way past the normal life and you should probably have them replaced very soon.
@Steve-O It may be possible that the switch from a 62 might be the same and GM changed it mid-way through 63. That might be a way to go. Worth checking out I think