Spin one wheel by hand whilst the car is out of gear,the handbrake off and the wheels are jacked up,have an assistant hold the other wheel,if either one of you cannot spin the wheels whilst the other is being held stationary then it is an LSD,if the pinion spins while one wheel is been held and the other rotated then it is a single spinner (conventional diff),the Fords I looked at have either a tag hanging off the drain plug which is a bolt on type in the EA's onwards I believe telling you it is an LSD and what oil to use whereas the earlier diffs like in the Fairlaines will have a rubber plug or bung which is orange or brown in colour and it will say something on it like :- use sub gear oil only.