Shims meaning the shim cap that goes on the underside of the lifter that is in direct contact with the valve tip. You set your shim height or clearance at its cold temp and at its hot temp should be approx. .003-.004" in expansion from its cold value. Typically its suggest you check your clearance every 15-20K. There is a lot more involved when running mechanical valvetrain vs hydraulic. More of the avid owners wont have any issue checking and adjusting during those periods where most others dont want to worry with it.
There is only one other manufacture for lifters for the Z that actually has a screw type adjuster that nearly eliminates the end user having to tear the valvetrain apart to grind the caps for clearance. These have a screw type plunger similar to your rocker arm locks that set your lash on a V8.
