Economical replacement rocker arm set?

OK on the lifters being all hard. Did you rotate the crank and test each pair one at a time to be sure that each lifter that you pushed on was on the heel of the lobe? If so, then that is one test of the lifters. It is pretty reliable but not guaranteed, as the operating pressure on the lifter is a lot higher in the engine running than you can push by hand. So you might not be able to push in a lifter with a 'sorta' weak check valve but the much stronger spring pressure (multiplied by 1.5) will be a lot higher.

And following up on the above suggestion to feel the rockers, see if you can locate the tick along the rocker shaft with a long screwdriver held up to ear.

That is a petty bad tick and it certianly sounds like a rocker. One thing I had not thought about is a bent or cracked rocker. It could be loose enough to drop a bit away from the shaft when the lifter is on the lobe. #7 intake rocker in your video is not holding oil in the rocker like the others; that is suspicious. Something is looser there and letting the oil drain out fast:
- the oil hole on the under side of the shaft is blocked
- the side holes are enlarged
- the rocker is bent
- the associated lobe is damaged
- the pushrod is short/damaged
- the lifter is not holding up.

You can do a similar type of test for a bent rocker. With each lifter on the heel of the associated lobe, see if you can easily spin any pushrod with 1 or 2 fingers, or if any rocker is really loose on its pushrod and on the shaft.