Thanks Spiros @fiveten and John @johnb They are much better than what I expected first, but mine are slightly larger and chunkier than the kit parts. It will look fine on the model.
I am sure I won´t make rare biplanes for a while. This project has been ongoing for too long. 🙂

I have just verified that the assembly jig is still correctly set. I can also feel that the whole plane will be quite strong once the upper wing is glued in place.
The model has many small flaws, but I really like this livery. It is not the usual “Soviet/North Korean night bomber” Po-2.

Livery looks perfect, Csaba @pikofix

I went through the archives again - this time the 1957-1959 issues of "Repülés", a Hungarian flying magazine.
My idea was to look up any information about the original plane in the news, sometimes the local clubs reported when an old plane was successfully repaired. I did not find anything there, but I spotted the HA-PAX in the background twice.

This photo was submitted by Tibor Janoska to a photography competition of Repules. The main subject was the Jak-11 in the foreground, but right in the middle of the frame, you can see the unique livery of HA-PAX.

The second photo was found in a longer article about the first flight of the R-23 Gebics. It was designed by Ernő Rubik, a very productive engineer. By the way, his son was the inventor of the big 80s hit on the toy market, the magic cube.
HA-PAX was the towplane of the Gebics on its maiden flight.

Great pictures Csaba @pikofix.
Your research delivers us some interesting information.

George, @gblair - it is the magic of internet. Many think that the internet is full with useless things, such as adult movies, cat videos, funny memes and similar strange stuff. But if a few motivated and determined people decide to use it properly, amazing things can born. One good example is this site, the iModeler. Great community, amazing models, lots of resources. Or there is Khan academy, a non-profit page helping kids learning all kind of different school topics, for free. When this pandemic started, I had a little bit of free time, and decided to dig into my family´s history. Without leaving my living room (abroad, 1000 km/600miles from my hometown) I was able to trace back 300 years in rural Hungary, all documented online. Many of those resources were available for free, others for a small fee (we are talking about less than 10 USD)

You are right, it is amazing what you can find online in these days. The amount of information online is mind-blowing.
I still remember the days, when my modeling references were old photocopies of even older photocopies from an old book, kept in file folders. Most of them were barely readable.

I am lucky enough to know multiple languages, it helps a lot when looking for something online. I speak Hungarian, English, German from school and because of my wife, and not so good, but usable Danish because I have been here for a while. The good thing of knowing Danish is that it gives me a basic understanding of the other Scandinavian languages as well. This language mixture really opens up the possibilities for finding information.

For these old Hungarian topics my main source is a non-profit photo collection of all planes ever registered in the country. These guys have a very active social media group as well, and share photos from other, less known photo collections.
There is an amazing service digitizing old newspapers and magazines published in Hungary (that also includes the parts from the former Austro-Hungarian empire). Their goal is to publish all newspapers and magazines ever printed in the country. I think I pay around 50USD per year for the service, but it is simply an endless source of information. All digital versions are indexed, so a simple text search returns a lot of results, and you can scroll through the thumbnails very quickly before opening the main page. It is surprisingly fast to look up information, especially when you use filters to narrow down the hits.
For these photos above, I went through a few issues of the magazine "Repules". First I did a text search of the type, opened up the pages, and read the text, but that did not give any usable results. The original plane was operating between 1957 and 1959, so I scrolled through the thumbnails of those issues. I only opened pages with photos of biplanes or gliders to see the details. The whole process took maybe an hour or so.
The unique livery and limited service time helped a lot to find information. In a few days, I will add more of similar photos to my Zlin thread here on iModeler. I used the same resources and methods to find those photos.

Finally, the model is out from the assembly jig, the upper wing and horizontal stabilizers are now mounted, aligned and glued (with minor incidents, I will need to touch up small areas with a paintbrush)