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I see we are competing who will post first! hahahaha

Right direction Kawboy, and scotch missed it! The truth is, it's original Kawasaki made, I guess for models which didn't need the emission control. It came of a never opened before cover. The plate is also of course original factory made Kawi. So, the factory was producing alternative covers with these holes blocked and a plate which would be placed instead of the reed valves. There is a gasket under the plate, and nothing else is blocked so the chamber is just dirty with some carbon.
Something I had no idea existed, and it seems like the exhaust mod is as simple as installing these, and have all factory made original at the same time!

It also solves the mystery of the gasket for the covers that came with the full gasket set I got from eBay. It had me puzzled for a while until I forgot about it. It just made no sense where would I fit it, and the key to solving it was to see those plates.

Another interesting show and tell is when you look at the underside of those plates, the side exposed to the exhaust gases. Clearly, the cylinders 3 and 4, which are the two most centrally positioned, are significantly more eroded than 1,2,5 and 6. I think this shows how these two are by default much hotter than the rest, which it's quite logical.

so essentially it is a reed-valve lid from the cam cover.

Po tate o / po tat o choke plunger/choke enricher

so essentially it is a reed-valve lid from the cam cover.

If your current 'rare' cam cover is essentially a cam cover, I guess that would be accurate.

Wish I had a pair of those, my imported (to the UK) A1 has a very crude rubber hose joining the two redundant stubs, which was on it in it's NY state.

My ailing memory also stands corrected on the AF ratios chaps!