I am considering swapping my 4.10s for 3.54's. Maybe a swap with someone or from a boneyard. Reason? Better milage and disc brakes. Is it a direct, lug to lug (entire housing) swap, or, lots of part swapping. Has anyone done this? Thanks

 

Without going too far into it, you will have to look at what to do with the emergency brake linkage. It is completely different. Also there are differences in the master cylinder sizes and you must remove the check valve. Best to use the master for disks. Now I don't know what it would do to your abs system.