First, thanks again for taking the time to post these. My first impression was, wow they have a nice shield on both sides of the meter. Gossen could learn from them. Then I thought the meter reminds me of that Keysight meter I ran with all the ICs on it.
It looks like they have the basic resistor, PTC then to the GDT with the two GDTs common in the center. I can't tell if that center axial part ties to the common point which wouldn't make much sense. I can't see the return path. If the board is still out of the case, maybe hold it in front of a light so we can see the inner layers more easily.
I have not found anything on the tubes they use but I'm guessing the 202 would be a 2KV part. It's difficult to say how it would hold up.
There appears to be some plastic from the case on the board.