Hi Martin,
Can you find out roughly how much road tax you'd have to pay with the xflo VS late model zetec?
I've heard the annual road tax for your car with the xflo could be as much as €2000
I would then talk to someone like emerald to see if they have an engine management that's suitable for use with a catalyst.
They would be abe to advise on what else you would need to make a cat friendly system.
I suspect the difference in reduced tax would more than pay for some thing like an emerald engine management and Jenvey throttle bodies or similar, fitted to a zetec
HTH BV