How did the inside of the old head look?
Deposits?
Color of deposits?
Oil?
Frayed inside edges of headgasket... etc etc.

Everybody adjusts valves their own way. I use a 0.020" feeler gauge
and set them to where it slides in easily but not loosely.
I usually go over them wherever it stops and adjust all that are loose
to 0.020+" , mark each rocker with chalk, turn the crank 180°, do it again,
and by the time I have turned and adjusted 3 times they are OK. I check
each formerly adjusted one the next time it is closed to make sure I didn't
adjust one that was just starting to lift to too small a lash and mark it
again. When they are all marked twice I'm done.

Remember that the pistons stroke in pairs, 1-6, 2-5 and 3-4. So if both
valves are slightly open on one of a pair, both valves will be closed on
the other one.
--
George Downs, The "original" Walrus3, Bartlesville, Oklahoma