I did something similar on my MK5 carb cvh. It's now running an OFAB turbo engine. The loom off a FRST was quite easy to adapt to my engine bay. Just needed to extend a few wires. I found it reasonably straight forward to mount the fuel injection and fuel pump relays near the battery.

Another pain in the ar$e you'll have to overcome is fuel. I changed my tank for one off a MK5 XR3i and raided the engine bay fuel piping from an EFI 90 spec MK4 XR3i, bought a new fuel filter and plumbed it in.

The place where the wiring links up to your existing car loom is behind the battery, just a simple multiplug. The only things you'll need to identify are oil pressure, rev. counter and ignition live etc.

Find full info on www.rsbible.co.uk

Good luck m8