Some early production, Lansing built 88's and Cutlass Supremes were built with the first digit of the code on the axle tube stamped incorrectly. Code 2AJ was stamped 6AJ in error (2.41 ratio). Code 8CB was stamped 6GB in error (2.73 ratio).
The letter code of AJ and GB is correct and may be used to properly identify the axle ratio.
General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.