To find the position for fitting the oil restrictor we have to look at the engine head from the intake side.
You should see a screw with internal hexagon in the engine head:
To fit the restrictor engine cam holder (E4 - the one straight over the screw) has to be removed as well as cam holder studs like in the picture:
Unscrew the bolt and fit the restrictor into the hole. It has to be fitted as pictured with the small hole facing downside.
Once you push the restrictor into the head it has to reach the stud on the opposite side of the head. Then you will be able to unscrew the long bolt from the restrictor.
Fit back cam holder studs and screw the bolt with internal hexagon back in. Job done.
Here are more pictures of how the restrictor works.
