Hi a S1 box will fit in a S2, but not the other way round as the MK3 Escort has a different mount at the front of the box which isn't used on the MK4. If the box is still in the car jack the front up, spin one front wheel, if it has a LSD the other front wheel will spin in the same direction. If the box is out of the car look where the drive shafts go into the box if there is a bar going from top to botton and you can see throught to the other side there is no lsd.

Hope this helps.