He don't use a grinder on parts that are not ours to grind on unless its body work. When customers have heads $3500 , rockers $2000, We modify the Head studs they only cost $100.
Drilling the head doesn't guarantee the stud is in the center and not blocking the oil feed holes . Yes if needed you can install a restrictor and know the exact restriction you have once the oil is sure to reach the restrictor under the rocker shaft. Or you can drill and grind and guess at your work.
Like the Edelbrock heads we just got in with the valve seat heights and spring pockets all over the place from doing them by hand with a New way cutter set. Using a precision machine with digital readout duplicates everything that is done to the same consistent measurement on every valve and seat. Steve just got a set of heads dropped off from western Pa. to install new seats to fix the valve heights .
Don't throw stones they may come back.