Ok, I have a Ford, but here are what my directions say:
4.3 Drilling and Tapping the Bulkhead Port
A port must be drilled and tapped through the differential housing to allow the seal housing tube through the housing to connect with the air line from the air compressor.
1. mark a spot for the bulkhead port on the right hand (seal housing) side toward the top of the differential housing that is in an area that will be well clear of the ring gear, the differential, and any other obstructions that may snag the seal housing tube.
2. Cover the drive pinion and axle tube areas with a rag to protect them from metal filings.
3. Drill through the housing swuare to the houside surface using an 11.2mm [7/16] drill.
4. Tap the hose from the outside using a ¼” NPT tapered pipe thread tap
5. Remove any sharp edges from the hole that may chip-ff and fall into the housing.
6. Very carefully remove rags and inspect with a service light inside the housing to insure no metal filings are left behind.
Hope that helps