You could be right, but the same technique was also used for patterns used in sand castings. Pieces would be fashioned and bolted together to assemble the final pattern. The reason I suspect that they were patterns is that there were no signs of wear / polishing that one would expect from a pulley. That being said, it these were spare parts, then they wouldn't have seen any wear either.
The other reason I suspect that these are more likely patterns is that the museum is not far from Galt, where the B&W (Babcock & Wilcox) South Works were located. There were a number of pieces that came from that company in the museum and there were a few drawings and other patterns around too.
http://www.southworks.ca/about.htm