I ran into this with my sport Trac swap. After some research, the EPA police does not have a way to tell if the ecu is a 97 or 01, so you can use the 97 motor and harness, and just say its a 98. The only difference between the 97 and 98 is pats, which is not in any of the engine wiring. You can run the 97 ecu and just say its a 98. Law states (for those states that enforce, like cali law) that an engine swap must be the same year or newer and retain all emissions devices, sensors, etc that came on the motor you are installing. Going with an older motor won't fly (the exception to those states that don't have emissions testing/enforcement), but since they can't tell what year an ecu is, not even hooking up to the data link will they get the info. Only the dealer has the capabilities to pull the year from an ecu. I got this info from a trusted source thats a certified tuner in an area thats on the border or an emissions compliant area, so he knows about what the emissions guys can and can't do...
SVT