I've collected 21 stud parts for quite a while trying to get one good block for my 36PU. I found a wide variety of heads of all descriptions. Water pump heads for domed pistons are not common. I think they were made by Ford to use on 37-38 engines with domed pistons to allow installation in 32-36 cars when using water pump block off plates on the block. I found one head that was clearly an aftermarket replacement head, it had a domed chamber. I saw other heads that seemed to also be aftermarket replacements, some resemble OE Ford on the outside, some don't. The chambers vary a lot in Ford heads. spark plug locations vary, the aftermarket heads vary even more. I suspect the aftermarket manufacturers sometimes cast Ford script on their heads, some have part numbers, some don't.
The Aluminum heads I've seen all were for flat top pistons, I've read here on the barn that assembly line 33-36 car engines all had aluminum heads, trucks had iron heads. All of the factory rebuilt engines I've encountered had Iron heads, so perhaps the new iron heads were a routine item to install on rebuilts and were cast for that purpose. My 36 had a Ford rebuilt engine in it, it had 1932 iron heads with 7/8" spark plugs on it. My guess is that they just paired up 2 similar heads and stuck them on as the engines went down the rebuilder line.
With you being located in The Netherlands my data might have no bearing on your situation, the OEM engines may have varied a lot from USA production.
I've seen enough identical rights and lefts that I don't think the different size chambers you have are normal. My direction if I were in your shoes would be to find a matching pair of heads or to find a match to your 82cc head. The average price for iron 21 stud waterpump heads here in the US has been about $25
If you are forced to use the heads you have, the 13cc difference might be just enough to make it idle a little roughly but I wouldn't bet a lot on that happening.