Thank you everyone for your feedback.
For the reference, this is suppost to be stock GM engine in 87 Caprice, which I own for about 5 years. Its now my weekend car, but as dd it servers me about 20k miles up to total around 150k miles.
Back to the problem:
Rocker arms clearance on one side of the engine is greater than the other one. The posted video was taken after careful adjustment of both sides.
Pushrods of some valves even lean on the wall in the cylinder head hole, which I do not like to see.
Today I checked everything carefully, the length and diameter of all pushrods are identical.I changed rocker arms of the "good" side and put them on the "wrong" side and vice versa. This does not changed anything, the allowance on the one side of cylinders is larger, then other side.
Therefore the reason is not rocker arms.
After closer examination I have discovered a mystery.
The "good" head have in the holes for the pushrods guide tabs on the sides.
The "bad" head have a circular holes and side allowance is therefore greater.
Both heads have the same part number, but 1 was in past exchanged for replacement part from 88 Caprice due the cracked head.
Excessive lateral allowance of the rockers would be diminished, if I install the pushrods with a larger diameter. Do you know if there are pushrods with different diameters?
I disassembled the engine for several oil seal leaks and also, when the engine was running, I was able to hear irregular knocking of timing chain. Therefore I wanted to check the rocker arms.
Now I wonder, if its worth to deal with this large laterel allowance, or not.
I appriciate the time you are spending reading and thinking about my problems, thank you