Interesting - that's very close to my Boler, which was also made in Winnipeg. Just a few trailers apart, by serial number. So it's almost surely a 1975. (Boler: "My long lost sibling!"
This reminds me that I've got the original brochure for mine -- it's not the same as the one in the document center for a 1975, so it might be neat to have it available. How can I submit it for addition to the Document Center? Just your basic scan to .pdf? (I don't have good access to a color scanner right now, unfortunately, but I can't think of another good way to submit it.)