OK, this is my first post on these forums and although I don't know a huge amount about the interior of Executive Brake Generator Van 913, I have some interesting info about the exterior that could make for a very interesting project. Executive Brake Generator Van 913 began life in BR as a Brake First Corridor, a Mk2b. When purchased by NIR in 1981, it became a standard generator corridor brake second. In 1989, it was converted to an Executive Brake Generator Van. This is where it gets very interesting. If you go to around 3:21 on this video
, you will see a Dublin to Belfast Enterprise arriving into Drogheda in 1993. Executive Brake Generator Van 913 is the first coach. You can see the vented windows. Now, if you fast forward a little to where the train is departing, you get to see the other side of the coach. You will see that it has Mk2d/e/f style windows!!!! The toilet window is still of the earlier type. This is because Air Con was fitted. It also makes for a highly unusual and unique coach. In 1995, it then became a generator brake first open and I believe it reverted to being a standard pressure vent vehicle.
So not much help on the interior but interesting info on the interior, I guess.