My Coach Yard 12-5 duplex sleeper required some major brass modifications.  To accommodate the upper single rooms, I had to drop part of the floor piece.  That involved cutting the floor into 3 pieces, adding some angle pieces and soldering it back together.  I also had to cut out and drop the floor support rails in the shell.  I was walking on eggshells the whole time.  Those brass cars are hard to find and expensive.  I got lucky.