Will a 85 442 8.5 rear end bolt right in to 87 cutlass supreme?

No, an 85 442 8.5" rear end will almost certainly not bolt directly into an 87 Cutlass Supreme. While both are GM G-bodies, there are differences in the mounting points and potentially the spring perches depending on the specific options on both cars. The width might also be different.

Even if the bolt patterns *seem* similar, you'll likely encounter issues with:

* Spring perch location and design: The location and shape of the spring perches on the axle housing might be different, preventing the springs from properly seating.

* Mounting brackets: The brackets that attach the rear end to the car's frame may not align correctly.

* Brake lines and components: The brake lines and other components may not be compatible.

* Axle width: The 442, being a performance car, might have a wider track width requiring modifications.

* Differential type: The actual differential components might differ and impact compatibility with driveshaft.

You would need to perform significant fabrication and modification to make it work, which would be a major undertaking. It's far more practical and less expensive to find a suitable rear end from a similar year Cutlass Supreme or other G-body model.