Originally Posted by Chip

The way that Tank Mike from Michael Woodford motorsport does it (he does more drive in drive out type conversions than I do as mine are normally on my car or my mates cars where we tend to just rewire everything on the whole car anyway, where as he is doing it for a living) is that he leaves the standard ECU in place for the immobiliser and the fuel cut on the pump when the engine stalls in an accident and to run the standard clocks with etc, and then just uses the Omex (his ecu of choice) to operate the injectors and coils.
Takes him and Jack around 2-3 hours to have most cars up and running on aftermarket doing it like that.