Hello,
I used the original plugs on the engine (injector plugs, cam, etc), we then used the loom that the haltech platinum 1000 series brought and meshed them together. If you have a good knowledge of stand alone computers then I would suggest you go for it. I have a buddy who has been working with haltech for quite a while now and he was the one who did all the splicing and merging. As far as the original ECU is involved I know Hoke from Hokeperformance.com used a donor car and used everything including the gas pedal and "BATS" system (or I think its called that, lol). Anyhow let me know if I can answer any questions.