Last time I checked Im sure cat was related to the age of the car and thus you wont need one as someone said above.

For efi, you need an engine and its manifolds and sensors, then the ecu and loom. This is where the difficulty comes. In an early non-PATS ford, or the vauxhalls I mentioned, the engine loom comes out separately from the car loom, they are joined only by a few wires, which are things like revcounter feed, ignition switched live etc and are easy to wire into a 1979 escort.

If however you use the PATS ecu and loom, it is far more integrated into the car, the wiring colours arent standard from one year to the next and the immobiliser is a nightmare. Like I say, having done both, I'd take the vauxhall engine any day unless you can find a cheap non-PATS loom and ecu.