Part of my plan for building Observation Car 150 is to make use of my existing masters / moulds for the single doors and the corridor end.
It isn't quite as simple as that, though. (When is it ever?)
The doors on 150 are a little fancier than your standard (3rd class) Superbarn, naturally.
The superior touch is the rounded corners at the top of the beading on the door.
What I have done, as you can see here, is to fettle two of my existing castings with some small pieces of shaped styrene glued in the corners which I will use as a new master.
I guess I must be getting lazy in my old age.