Under valve cover ticking

Adjust what? The hydraulic lifters?
They normally don't need adjusting except after a rebuild, etc.
There are several things that can cause a tap and the tap is most likely the result of too much lash in the valve train for one of more cylinders.
The first thing is to narrow it down to which cylinder by performing a cylinder balance test and listen to the change in sound of the tick. What you basically do is cancel each spark plug wire out one at a time.
You could wear a pair of gloves and use an insulated pair of pliers and pull each spark plug wire off the distributor cap if they actually come off.
Then once you narrow it down to which cylinder or if you already know which or even which bank, remove that valve cover and see if anything obvious is wrong. Then check the camshaft lobe lift of each lobes on that cylinder and compare to another cylinder to see if maybe a cam lobe is worn down, cause that will cause excessive lash. It could also be a bent pushrod, a pushrod worn down on either end, a collapsed lifter, a rocker arm stud that has pulled out of the head, a broken, cracked or loose rocker arm and a valve that is not seating because of carbon buildup on the stem preventing the valve from seating fully.