Just a FYI, even if you get the stock NAV unit to work they are locked to the VIN of the doner car and will need to be re-programed by the dealer to your VIN to receive updates for the maps and the OS. But since your VIN does not have the NAV factory installed the dealer will tell you they can not update the OEM VIN database and they can not update the unit or enable map updates. I would highly advise you pick up a Kenwood Garmin based NAV unit.
Even if you can change the VIN in ForScan when you order the map updates from Ford they will not sell you a update since the the Ford database shows the VIN did not come with the NAV from the OEM VIN. You should see the months of emails I have from Ford HQ about my SYNC 2 NAV to SYNC 3 NAV update that will not allow me to purchase maps for the SYNC 3 NAV since Ford's database shows I have a SYNC 2 NAV from the VIN database.You can update this via Forscan if you have the VIN from the donor car I'm sure, or the ASBUILT data info to just add the lines into your ECU.
Even if you can change the VIN in ForScan when you order the map updates from Ford they will not sell you a update since the the Ford database shows the VIN did not come with the NAV from the OEM VIN. You should see the months of emails I have from Ford HQ about my SYNC 2 NAV to SYNC 3 NAV update that will not allow me to purchase maps for the SYNC 3 NAV since Ford's database shows I have a SYNC 2 NAV from the VIN database.
How would Ford know?