yes you can fit the ATB diff , with the uprated box this is £1k.

somehow i dont think the diff is at fault with the escorts handling!!

a 200hp escort is fun to drive , i have one, not trying to put you off one just making you aware before you dive in

a nice 330hp 4x4 sapph is a much better choice for drivability and general performance but not a patch on the S1 looks