I get that the post was made 3 years ago, but is that observation car private?
The observation car is payware from Paulz Trainz but the textures have been heavily tweaked by myself as the original textures from Paulz were dreadful! It also comes with incorrect bogies from Paulz.
If you decide you're going to get it then you'll need to contact Paulz as it doesn't appear on his website. You will need to ask him to fit the correct Gresley type bogies, luckily, I have the Gresley bogies from another of Paulz models.
Tweak the textures to your taste if you so wish.
Best of luck,
Rob.