The arms are not the same as on a standard Sierra.
- The pickup points for the arb are most of the time not present on a standard Sierra.
- Arms for cars with drum brakes are different than disc brakes. Arms for drum brakes have a too small hole for the driveshaft and won't have a location for the ABS sensor either
- The angle for the plate for the hub is at different angles to give different camber settings depending on model/ride height.
- As said, the bushes for the Cosworth are spherical bearings but the fitment of the bushes is the same for all arms

I believe 2wd sapph Cosworth arms are the same as 4x4 Cosworth arms, but 3dr arms are different.