The engine loom is separate. It connects with one wire to the fuse box, and that is it. The 3i loom will need 2 wires cut and swapped, and has no wiring for the Amal valve. You can run without an amal, get something like GReddy or apexi instead.

Details of the wires that need swapping can be found at http://www.chardcars.co.uk/

There is also a thread in Fiesta-Turbo.com...however, the details seem to be a bit mixed up. I have my own notes and a few wiring diagrams, PM if you want them.