Originally Posted by 66tempestGT
im no expert but i cant imagine why two different castings would have the same casting #.
This is from the PY Forum. It seems that GM did use the same casting for BOP. Not everything is as simple as straight forward as you may think.
"Olds for sure and maybe Buick also apparently did share the same center casting.
9779822 is a Pontiac engineering issued part no. It is for the casting only and does not identify the Axle Tubes & Diff Housing assembly.
What I do not know is whether Olds (or Buick) used different axle tubes pressed into the center casting. So I cannot say if a '65 Olds Cutlass rear Housing is completely identical to the Pontiac. Possibly same Housing Assembly but different ring & pinion gears were offered, I just don't know anything about Olds to be sure."