When I was communicating with I believe his name was Mike at CWI, he told me the casting number were worthless for the most part. He wanted a physical description of the outside, seems a primary difference is the number and pattern of the reinforcement ribs on the outside. Below is a pic of the exterior of mine which turned out to be most likely from a mid-80s XJS with tapered bearings, and was actually a Dana. The way he talked, the only real way you identify them was open them up. The stamped tag bolted to the rear cover is helpful in identifying the ratio, as well as if it is an open or a BPL PowrLok diff.
