Its a manual process on these, as the full ECU controlled immobilser system was fitted from about 2002.
Thanks for your time and help with my 2000 Iveco 2.8.
The issue was resolved by removing the immobiliser and rewiring the stop solenoid.
I will put together some info but in case you get any other enquiries, a couple of quick points.
Removing the immobiliser is really easy with a Dremel tool, cutting disks and grinding head. Took only a few minutes.
The original power to the immobiliser can be utilised to provide power for the stop solenoid without adding a new switch/wire, and continues to work from the ignition.