All (’76-89) FMJ-body differentials are interchangeable – with a couple of minor differences.
The ’76-81 FMJ 7¼� came with 2.5� (63.5 mm) tube diameters.
The 7¼� differential tube diameter bumped up to 3.0� for ’82-89 M and J bodies. The ’82-89 7¼� and all FMJ 8¼� use the same shock plates (3.0� (76.2 mm) axle tube). The 76-81 7¼� differentials use a different shock plates (both parts/both sides - see red circle, below) because the axle tube diameter is smaller.
If you are replacing a 7¼�...
FMJ Differentials
