It's interesting that there are 2 styles of these, the one on the left side is what has been used on Yamahas and Toyota engines for a long time, in fact I think that Yamaha pioneered this style of bucket tappet + shim valve actuation and designed cylinder heads for Toyota (and others no doubt).
I had a 1989 Toyota Corolla GTS with the 4AGE twin cam engine and it had that style of valve lifter. To check them you just use a standard feeler gauge but if any are out of spec, there is a special tool that you use to compress the lifter and then use a magnet to pull out the shim. You then measure the shim with a micrometer and have to figure out what thickness shim you need to buy to get the adjustment correct. All this was detailed in the Toyota factory shop manual. Mine were in adjustment thankfully but my take on this is that mechanics rarely if ever adjust these unless there is an audible tapping noise coming from the valve train. It's just too time consuming. The real issue is if the clearance is too tight, which can lead to burned valves. I have heard that Toyota techs never adjust them, but don't know if that's true.
So yes you can check em, but if any are out of spec, you have a time consuming job on your hands
The other style on the right looks like you'd have to remove the cams to change that style shim.
This makes you appreciate nice quiet hydraulic lifters!
