It's years since I did anything with hydraulic lifters - that was on a Rover V8 back in 1991.
A hydraulic valve lifter works by, basically, filling with oil. The oil pushes up the 'bucket' or cup - to make contact with the tappet pushrod -or in the case of overhead valves - the lobe of the camshaft.
Sometimes if a car is left standing for weeks, the oil drains out of the lifter body and at start up can sound like a bag of nails bouncing around an a bit of corrugated metal. As soon as the lifter fills with oil and self-adjusts the tappet/valve clearance, the noise stops.
There is no possible adjustment with hydraulic lifters.
If you've reground the valves there should be no problem with the self-adjusters which will automatically set the valve gap.
It's difficult to see how a valve stem can be too short -if you've had the head overhauled - skimmed/new valve inserts put in - it will be due to the tolerances having changed, or even how the camshaft is torqued down.
An example of this is the old Rover 2000 1960s style. It didn't have hydraulic lifters but it did have an overhead cam using a bucket and shim arrangement. After a cylinder head skim and retightening the camshaft down, all the valve clearances between the lobe of the camshaft and the top of the 'bucket' were gone, simply because the head had been removed, overhauled and refitted. In this instance it was necessary to remove the camshaft and buckets - then take the shims to a machine shop to have a certain thickness taken off. Then repeat the job of putting the camshaft back ... measure the clearances.. go to the machine shop again to have the shims re-skimmed ..
As for the limits of self adjustability, unless somebody writes in to say otherwise, I believe that in the most general of terms, 60 thou is the maximum lift.
This place won't let me post any URLs ... but if you do a Google search for:
'bucket and shim'
and
'how a hydraulic lifter works'
..you'll find a lot of images and explanations.
