The biggest difference is Ford paid a form of tax to CARB for permission to sell it in CA.

I'm not sure there are ANY physical differences any more.

On the '99's, there was the second post-cat O2 sensor, but I suspect all may be getting it now. It is actually handy to have this second O2 so the PCM can monitor the function of the catalytic converter and warn you if it is failing.

And I am not sure about any of them getting EGR's anymore. Although EGR's are great for part throttle performance, fuel economy, and emissions, they also tend to be a relatively low reliability device compared to most systems on modern cars. They do have a tendency to get dirty or fail within 200K miles.... which is considered low reliability these days! Do away with it, do away with warranty repairs and customer complaints.