You have the cam lobe in the same position (i.e. the nose pointing away from the rocker) and on the flat shim, just use feeler gauges as normal between the shim and the rocker arm. On the slotted guide you'll need to cut down some feelers in order to get into the contact area. The valve clearance should be 0.21 - 0.26mm (cold).
On re-reading the book, it looks like Nissan tell you to replace the rocker guide (the slotted shim) with a flat one for the purposes of setting the valve clearances and use standard feelers, but that might not be practical for you.
Correct camshaft clearance is 0.14 - 0.17mm (cold), check this first and if it's out of spec. then start playing with the valve clearances. Book says you should be checking at the edges of the cam lobe, not the middle (in the area approx. 3mm from each edge of the lobe).
Hopefully that helps!