What I would do is use the complete DC2R engine harness + the section of the chassis harness that runs to the ECU (you will have to slice this out).
This will basically connect Engine > ECU

From there you will have to wire in (at minimum) the following to the ECU from your kit car:
-Voltage Backup
-Brake Switch
-Fuel Pump Main relay
-Starter Switch signal

From the driver side of the engine harness:
-you will need to supply 12v ign power to injectors, o2, iacv, vss, alternator
-these sensors go directly to cluster, RPM, Coolant temp, Oil pressure switch

You'll also need to wire in the Fan Switch directly and disable the ECU immobiliser if you're using an AUDM P73