I looked into this myself a while back just to see if would be feasible. There are two main problems.
1) - the engine is quite far back in the engine bay in the Focus. Unless you are willing to get rid of the A/C line that run along the top of the firewall, your total induction length will be very short. This is not good for usable torque.
2) - the factory engine management system will be thrown in the trash as MAF based systems cannot be adapted to individual throttle bodies unless you run a large plenum and a snorkle. The plenum, without huge testing and development can negate a lot of the work that you have put into your shiny new throttle bodies.
This is the way to go for good power. Mr. Zetecinside has some excellent details about throttle bodies at
ZetecInisde as Michael indicated. Also.
Jenvey in England has a lot info on this sort of induction system.
[ 09-02-2002: Message edited by: teamDFL ]</p>