I'm using both factory computer and a V4 Wolf 3d. The 3D is out of a mates Soarer and was wired in piggy back style, no need to remove the engine loom, just 3 injector triggers and 3 ignition triggers with plugs so you can run either wolf or factory in either ignition or injection, great for fault finding and retains driveabilty. The rest of the Wolf was externally wired. I'm planning on making some turbo dumps prior to fitment as well. The one thing I would like is some clearer wiring diagrams if anyone knows of a source.
Classique71, I like the Lexcen idea, but the car is actually really nice(a change for an old commo) so I don't think I'll drill any holes in it(except for the intercooler pipes).