ok heres a model i do know alot about xc's.
ALL xc radiator support panels are the same throughout the model run.
ALL xc headlghts remained the same update or not throughout the model run and are as follows:
ALL xc fairmonts/fairmont gs/gxl had square headlights update or not.
ALL xc falcon gs/rally pack had twin round lights as per the gt apart from quartz halogen head lights which were unique to the xc gs range standard on the falcon update and optional on the pre update.
hope this helps u out.