Well, if your clutch was the original style then it was a 9". The good news is that the 9.5" clutch will work fine in the 88". I replaced my original 9" clutch with the larger 9.5" version in my 88". You'll need to order a (newer style) pressure plate for the 9.5" clutch, the clutch itself, and probably a new throw out bearing for good measure. There may be a few other small items I'm forgetting, but any good parts supplier can tell you exactly what to get.
Be sure to check your master cylinder and slave cylinder.
61 II 109" Pickup (Restomod, 350 small block, TR4050)
66 IIA 88" Station Wagon (sold)
66 IIA 109" Pickup (Restomod, 5MGE, R380)
67 IIA 109" NADA Wagon (sold)
88, 2.5TD 110 RHD non-hicap pickup
-I used to know everything there was to know about Land Rovers; then I joined the RN Bulletin Board.