Do you have photos or
do you know YouTube videos
about Three Passenger Cars?
Prototype: Swiss Federal Railways (SBB-CFF-FFS) older "standardized" designs. Type AB4, 1st and 2nd class. Type C4, 3rd class. Type F4, baggage car.
Model: The cars have inset roof vents. The diaphragms can be changed. Total length over the buffers 67.8 cm / 26-11/16".