Not really any help but I always thought on the newer models almost all was tied into the immobiliser system including the abs module.

I'm sure I've read somewhere that on Insignias the a/c module is also paired to it but I may have imagined that.

I think even on the earlier Vectra C SRS module was tied into immobilise somehow.

Unless you can fit the 2nd hand ecu and read out the VIN number then apply for security code to reset it then code into car if you know the security code for his own car.

Not even sure if this can be done like on previous models.