FRS dials need ecu to control them sadly, box is best to be a focus rs one due to bellhousing being better for focus cover fitting as standard zetec clutches won't last at all. standard zetec clutches aren't designed to run on turbo engines, the torque will be massive.
you could run an rs2k box and fit the diff to that, clutch could be awkward as the bell housing inside is a little smaller.
personally i'd just find a FRS one and flog the diff, shot peened gears in the FRS ones too