As with lots of functions, just because the loom has redundant plugs doesn't mean that the rest of the hardware is there waiting to go.

Its extremely unlikely that you have any ABS pump/valve block in the engine bay, and no ABS system would be installed for only 2 wheels.

I've done several rear disc conversions on non-ABS equiped Focus with no problems on brake balance. You shouldn't have any problem if your swapping the stub axles/hubs. Its the suspension arm bush bolts that seize solid and have to be cut off if an air gun doesn't shift them.

Have fun

Martin