Boxxy,long shot but do you have "anything" in front of the radiator inlet opening like spot lights etc... I saw the same symptoms on a car that had had an engine conversion and depsite swapping everything at speed the car overheated......
Turns out the spots lights were stopping/interfereing with air flow... Removed spotlights = no overheating....
Took days looking for the problem to find it was right under his nose!
Spookypt