Scott,
  Most pulp mills had a small storage area for cars - maybe 15 to 20 - so you could model
that yard and put the entire mill "on the backdrop" ... perhaps even do some selective
compression of the size of the yard (number of tracks wide and/or length of the tracks).
  I've seen brass pulpwood cars selling on eBay for very little money - a bit on the slim
side in terms of details but nonetheless serviceable - especially after adding a few
small details and weathering them.  Pulpwood hauls were short - usually less than a
hundred miles and often less than 50 ... so it fits in with your "no longer model a main
line" ...
                                                                                               - Jim in the PNW