A pre-1995 Zetec should not cause problems at IVA. With a post-1995 one you would need a cat, so bike carbs are not an option any more.
With regards to chassis clearance, the Zetec engine has a plastic thermostat housing stuck to the back, which conflicts with TR8. You can push the engine a couple of cm forward, but then Type 9's gearstick impinges on TT5. What I did (and spud69, apparently, too) is cut out a section of TR8 and double it up with another piece of 25x25 behind it. You can see it here if you look carefully:
Moving TT5 is another option, but TT5 is also where the dashboard panel ends if you extend it all the way to the tranny tunnel. Another issue with this route is that the reverse switch plug is hidden behind TT4.
If you have any Zetec related questions, I'd be glad to answer them.