as looking at the clutches there are diff models...
http://www.ebay.co.uk/itm/Citroen-Sa...item1c1c93721a
or
http://www.ebay.co.uk/itm/Citroen-Sa...item1c1c93722a
Their both the same dia, and guessing if the splines were different, then the boxes wouldnt be interchangable...