@HermannB - Interesting. It is a totally different hitch set-up. I wonder if the guy from Cults3D could design it and add it as an option in the files.
For the decals, they are quite easy to make. Get some computer decal paper and design away. I used Testors clear film paper this time’ but have used others as well. As I said, I design the decals in PowerPoint. Then I print a test page on regular paper to confirm size, font, etc. I then cut a piece of decal paper slightly larger than the area of decals I want to print. I use scotch clear tape to tape the piece of decal paper over the area I want to print on the test paper; seal all edges so the print head doesn’t catch the decal paper edge. I then run the piece of paper through my inkjet printer (make sure the paper is compatible for your printer - they make inkjet and laserjet paper). Once the decal paper is printed, let the ink fully dry for about an hour. Once dry, spray the decal paper with clear topcoat (gloss or flat) to seal them; let this fully dry for an hour or two. Once dry, carfully cut the scotch tape to release the decal paper from the larger sheet. Then cut out each decal and apply like any other water-transfer decal.
This thread has a good discussion on them. If you search for printing your own decals, there are quite a few topics on them as well.
Nothing special to making the air hoses and brake cable. I use black 1/24 scale spark plug wire. Cut to length and glue it coming from under the frame. For the gladhand connectors, I have 3D printed ones from our own James Lee (@Petition2God). I add them on the end of the airlines. The brake light cable is the same with a piece of 0.060 rod added on the end as the connector.