Vitz noisy rockers/head

[gonk]

Hi,
I'm new here and trying to get some advice and info on my Vitz.
I've recently acquired the car a 1.3 2SZ JDM (I think).
Basically when its running it sounds like a troupe of monkeys hammering anvils up around in the head. I've just taken possession of the car and its done 55000k - I suspect it recently had a thrashing by a previous driver - drove it like they stole it cause they did.

One of my first steps to try to figure out where the monkeys and anvils came from is to take the rocker cover off and check valve clearances.

If anyone has any experience adjusting/measuring valve clearances on these your advice would be very much appreciated. I've spoken with the local Toyota service centre and they said they had never done a valve clearance check and adjustment on one of these so I'm a bit reluctant to take it to who should be experts and pay the price for their first experiences.

Here are links to photos.
Main photo of where I'm trying to take the valve clearance - there's not much room so looks like I'm going to have to somehow customise some feeler gauges unless I've got the measurement location completely wrong?

https://datasensic.net/vidahomes/tappetrollershimed.jpg

Over-all head and timing chain images (I now realise painted timing links migrate and are really only useful during initial timing setup unless you want to keep winding the engine over till everything is synched. TDC no1 can be found by cam lobe inspection and crank and cam timing marks - or maybe I have that wrong too :).

https://datasensic.net/vidahomes/headcamholders.jpg

https://datasensic.net/vidahomes/headchainmigration.jpg

Thanks for any help in confirming the way I'm attempting to measure valve clearances .