I've been learning how to model number 11's cylinder/saddle casting in TurboCad using the detailed drawings developed by Jason. First, I modeled the cores:

The cores are: red - exhaust, green - live steam, light blue (and underneath dark blue) - main lightener, tan - frameway, brown - cylinder bore, dark blue steam port, darker green - outer lightener. My model represents only one quadrant of the complete assembly - the left and right cylinders are identical and formed from the same molds; the individual castings are symetric fore and aft, so only one half is modeled.
Then I encapsulated the cores with the casting outer shell:

I then subtracted the cores from the outer shell to represent the final casting with voids where the cores had been, and then I split the casting into 5 pieces so I could inspect the inside of the casting at various points, as you can see in the picture. You can not see the interior details unless the casting is opened up.
Finally, I sent the CAD file to a 3D printing company called Shapeways, and 5 days later the UPS guy brought me little plastic pieces!

My design is on the Shapeways web site and you can see the model here:
http://www.shapeways.com/model/952269/cylinder-study-2be.html?li=my-models&key=15c6a8ee31134438744f6510c95a0906If you click on the right arrow or the shaded cube the model will revolve for you. You can actually follow the live staem and exhaust passages as the model revolves.
After I had studied the 3D printed parts for quite some time, I found a small number of errors that were hard to find in my CAD model even when I could see them in the plastic model.
I started this effort last fall - it took quite some time to become familiar with 3D modeling with the TurboCad software and quite a while to become comfortable with Jason's design.
I'm currently working on the outer shell molds and I am trying to get some more parts to the 3D printer soon. This is a very complicated casting and it hasn't been easy to get my arms around it, so to speak.