Is it possible to run throttle bodies on a zetec but still keep the oem engine management as my mate has a focus so don't know how you would run aftermarket management

I imagine you could with a little imagination but would need to retain the MAF so effectively you would replace one large TB with 4 smaller ones.

The volumn of air entering would not scale for small throttle openings, so not really worth the effort.

Aftermarket management replaces the ECU, nowadays these also tend to be tied into the security systems and dashboards so keeping the car feeling very original may not be that easy.

its possible main issue is need to still run a common plenum across the throttle bodies to maintain the MAF sensor

Works ok for me on a 1.8 with early non pats ecu. It is pretty sensitive just off idle as Mark suggested, which makes it difficult to drive smoothly below 30mph.
I've got a wideband which shows it seems to cope ok with all the changes although it's probably not running rich enough for peak power

Zetec plenum