No you got it rightI am confused.
If toyota is selling a replacement 80 series steering box with a 105 sector shaft, this would require a new pitman arm as well. As the pitman arm from the 80 series takes a smaller diameter spline. The strength of the 105 sector shaft comes from using the same diameter shaft into the (105) pitman arm. Where the 80 sector shaft diameter is reduced as it mates with the splined area of the smaller pitman arm . The smaller diameter 80 series shaft breaks (if/when) just above the pitman arm.