It's possible that the ECU is the same, just different options turned on/off. It's also possible that the existing harness in the cheaper Focus has the same engine wiring harness as the higher optioned versions. If so, the plug should be there waiting for it.
The challenge is going to be ECU programming.
2014 Mustang GT custom ordered to replace the GT500: Sterling Gray, NAV, Recaros, Brembos, Glass Roof, back up camera, 6 speed auto, loaded
2012 Focus Titanium - 18" wheels with handling package
2009 GT500 Shelby (700 rwhp) - sold