I loved this mod. I'm not a lua programmer, but it looks very well done. I was trying to add a rail as well but I couldn't, it would be very useful to me. I added the file with the same name to the folder, and added it to the VANILLA_ITEMS list. but it did not work. Do you know where it could be missing? Or if you want add you can use this png.
https://drive.google.com/file/d/1tadfzxX-TiFDuPxD1hP7NdnelitaUDfh/view?usp=sharing