Yes, it's the center carrier. Simple swap, disconnect the driveshaft, unbolt the axles at the hub and pull the axles out a few inches. Then unbolt the carrier, it should fall out so have a helper with a jack. Put the newer carrier in and bolt it all back together. For gaskets, tell your parts store to look up a 71 3/4 ton HO52 differential.
You need to find a differential from a 64-72 3/4 ton. Two ratios available, 4.10 and 4.57. THe 4.10 is getting a little hard to find, but they are still out there.
