Good news and bad news, this seems like a joke.
The good news is that there are monitors with plastic housing, and that therefore weigh much less. This monitor that I am testing is a metal case, which weighs a lot. The same with plastic housing weighs less than half.
Also, I'm studying replacing the 13-inch monitor with an 11.6-inch monitor, with this size I can put the monitor very close to the hole in the playfield, and so the bracket would be much more compact, with shorter straps, and easier to manufacture and mount. The problem in this machine to install the monitor very close to the hole, are the two coils that are on both sides of the hole that limit the maximum width of monitor + bracket. I have that measure, and I just need to check if an 11.6-inch monitor without housing, or even a 10-inch with housing can be installed in this way.
I'm going to order monitors of 10 and 11.6 inches, always IPS and with HDMI. The resolution can be Full HD, but for these small sizes, even with 1280*800 it has to look very good. Keep in mind that with a 13-inch monitor, even Full HD, only part of the screen is seen through the hole, so in practice the number of lines and columns is less. And if we put a monitor of 10 or 11.6 inches, very close to the hole, which practically the entire visible area is going to see through the hole, although it has less resolution, in practice it is the same.
And the bad news, the Chinese are on holidays all the next week, so I will not be able to manage the order of the 10 and 11.6 inch monitors until then, especially to be able to test if they fit well in the hole, without touching the coils, to design the final bracket. Meanwhile I will continue testing with what I have.
As for Eyoyo, it is not a manufacturer, just one of the many Chinese companies that buy from several manufacturers and label the products with their brand. Now I have contacted another Chinese supplier, who claims to be a manufacturer, and offers me monitors with plastic casing at a very good price, in addition to a cheaper shipping cost, although this may be because they weigh less as the plastic casing.