First, if rocker arms and/or rocker arm shafts are worn too badly, you will never be able to adjust them. There will, in those cases, be high points and low points in the bearing surfaces, and when you have adjusted the "loose" portion correctly, the rocker will move to the tight position and the lash will then be too tight, and vice versa. If you cannot get rid of excessive noise and your adjustment nuts are not too loose, then check the rocker shafts and rockers for scoring and wear.

Regarding the Argentine blocks, I will try and post a picture here. However, if it doesn't post, the heads look like Y Block heads except that the intake and exhaust manifold mating surfaces look like they've been taken from a 289, and the combustion chamber also looks like a 289 chamber.

The block looks pretty conventional. It is clear from the picture that the lifters are like USA Y Block lifters, and the front of the timing chain area shows no evidence of hydraulic lifter oil galleries. However, I'm not sure whether these heads are mounted on an American block or not. I do recall seeing a Y Block block that was set up for hydraulics, but then, I don't even know what I had for breakfast...

It is clear that these were the engines that the famed WEslake heads were made for, since they would have the same cam lobe order needed for the Weslake heads, an oder that the USA version Y wouldn't work with.

(nope, can't get the pic to post, sorry!)