The carriage ends are normally quite simple but 125 requires a bit more brainpower because they are not identical.
The trickiest aspect is accounting for the difference in their width.
The problem is that one end of the carriage has the vestibule doors inset as on a regular Superbarn saloon while the other is at the full width of the body.
I've had to make some calculations (and cross my fingers) to hopefully ensure that when it is all joined together the two body sides will be running parallel and it's not narrower at one end than the other.
At the point where my brain started to hurt I decided to stop theorising and just cut some styrene and see what happens....