Sorry, I'm not an expert on this, but Checking the old Pathfinder seems like it would be your best, cheapest option. For the second gen axle, I don't know if it's the same width as the older Frontier, and the bolt pattern is different. You'd have rim issues. If the Pathfinder is a solid axle, then it might not be too hard. You will need to check into a proportioning valve, and possible master cylinder from the pathfinder, because of the pressure difference used between drums and disks. But something to consider when doing this is the parking brake. Most rear disk systems use a drum setup in the disk itself. That too cakes up with mud, and will require regular maintenance. Good luck, and let us know about the Pathfinder parts. Sounds like a good project.