If you're going to get this system working you'll also need the RS1600i flywheel and gearbox sensor.
You'll also need the get the hole precision drilled into the bottom of the gearbox to fit the sensor in, - the fiesta's box won't have the hole. These sensors can be an absolute nightmare and have been the cause of many rs1600i owners converting to a distributor.
Are you sure you want to ditch the Fiesta's EFI in favour of the older system used on a 1600i? You could put the head off your RS1600i on the Fiesta's original CVH with some work. The 1600i bottom end is standard XR3.