All I know is that the tensioner on a standard 300tdi is out of alinement to the other pulleys which the cam belt runs on .and the mod is to realign the pulleys with a modifiaction done to the tensioner, I undertstand that all tensioners for a 300tdi have had the mod embodied.
So just have look if you can at the cam belt and if it is inline I would say it has been done.
hope this helps