There is a way of telling, Ive seen it mentioned on threads on here, but cant for the life of me remember how. Something to do with fins on the casing or some such
AFIAK the Hydratrak is a supposedly better slippy diff than the standard one. I thought if you diodn't have the Hydra track option it came with the BTR or GKN LSD diff as fitted to Chims/Griffs.