There are about 4 versions of FWD M66 boxes
P1 Volvos (S40/C30 etc) and Mondeo XR5 have the same gearing.
S60R and Focus XR5 are geared differently to the above.
I think there's a couple of other minor differences.
You can probably choose any of them but just be aware of the differences to make sure it fits and you get the gearing you want.