Here is what I found from previous post and from a way more experience dude than me. Original post is for a 750, but the procedures make it more understandable for the less experience people, like me anyway. Keep in mind that the clearance for the 750 is .10-.15mm for the example, but yours, like Nessisim says, is .10-.20mm for inlet and .15-.25mm for outlet..
There are two ways at least to check clearances. I don't have a KZ550 manual either, but the first thing to do is lock your automatic tensioner so it stays adjusted throughout the procedure.
The first procedure that is the generally accepted method you'll need the manual. You align a timing mark a certain way and check 2 valves. You need every available feeler gauge size from .01 to .25mm. Insert each feeler until you measure the exact clearance. Move the engine to the next specified mark and repeat on 2 valves, and so on until all 8 are measured, then take your readings and add or subtract shim sizes that are available in .05mm increments to get the correct clearances.
The other method that I was taught 30 yrs ago from a factory Kawasaki mechanic is you basically only need 4 feelers, a .05mm, .10mm, .15mm, .20mm. Lock your tensioner as in the other procedure before beginning work, then pick a valve to check. Turn the engine over slowly by the 17mm nut on the right end of the crank while you contantly try to stuff a .10mm feeler between the bucket and cam. If it goes, try a .15mm, if not try a .05mm. Find the largest in these feeler sizes that will insert during any spot in the rotation of the cam and call that your clearance. Repeat on each valve. Now you have all your clearances checked and all numbers make sense in shim sizes available, so calculating is no problem. So if you measured for an example .10, .10, .05, .15, 0, .10, .10, .10 you would see that chances are swapping a 1 size smaller shim in #3 would bring it to spec and increasing one size on #4 would do it there. #5 is the question mark and probably going down 2 sizes on it would do the trick.
The same engine checked by method #1 may read for example .12, .11. .08, .16, .02, .14, .13, .10 This just is checking too close as since the shims are only available in .05mm increments, the same exact swaps would be needed, just a different way to accomplish the same thing.