I believe the 110mm is the inside ID of the ring gear and these were used up until 1977 then the ID changed to the 115mm version. If you have the ring gear off then measure the centre ID it should be 110mm if a standard 240z diff - if a later 260z/280zx/S12/Subaru etc R180 it will most likely be the 115mm version.
Now you might notice I dropped the word Subaru in there - yes Subaru are still using the K aka 115mm R180 Longnose diff today - however they have different input shaft splines the Datsun stuff is 25 spline and the modern Sub stuff is 27 spline. However you can use the later model Sub R180 longnose in your zed you just need custom input shafts that mate to the stock half shaft - a place in the states makes them called Beta Motorsport
So you need to confirm what you have and what that Quafie on Trademe is for.
