Thanks for putting the pictures up Stephen, and thank you all! I'm looking forward to bringing the patterns up to the museum this May, and getting the chance to meet and work with everyone.
Mike, the piece in the middle is a "core box". It's used to ram up the sand to form up two halves of a cylinder to create a core, which is used to create holes in the castings. I would imagine sometimes core boxes are a final dimension, but in this case, it's to aid the machinist in boring out a larger hole for the bearing in the pillow block. The painted yellow sections tell the foundry that there is to be a core placed in those locations once the halves of the mold are rammed up, and the patterns removed. The core box is painted yellow so that they know that it's a core box, and not something else. Bernie has made many more core boxes as well, including for the counterweights, he can also correct me if I've misstated anything, or not made sense!