The layshaft and crown wheel should be a pair as ford has used so many different ratios and toothsizes. The S1 crownwheel to diff attachement is by 6 bolt where as the S2 has 8 bolts. This means that we have a problem. You can take the crown wheel and drill four new holes and tap them to M10x1, but I warn you, that material is pretty hard. Better find a different diff or a matching layshaft/crownwheel combination.