"Newer R180s are availabe from the 84-88 200SX and have a[glow=red,2,300] large K [/glow] cast into the top of the housing. They can be used in the Z with some modifications. The newer diffs use a stub shaft that plugs into the diff and is retained by a circlip, and the older diffs used a bolt in stub shaft."
About 7th paragraph down, then goes on to explain "Modification procedures to convert new K R180 to bolt in stub shafts"
Posted the link for other peoples sake as well, it's a good read.