Bill, two comments;
1. These were large drawings, probably on Mylar or sepia based on the timeframe. From those master drawings, scaled copies in blue print and other formats, was possible. I made some drawings for Ford of some of my designs in the late 80’s. The drawings were billable deliverables, and owned by Ford.
2. As improvements (better ideas, cost reductions - whether better ideas or not😎, etc) were done, they were implemented and approved as revised (or new) drawings. What we should expect in the Osborn reproductions is that the latest versions, which would be most prevalent 20+ years after the fact, are what we are looking at. As we traverse back in time towards the beginning of 67 production, we need to be very careful when interpreting those drawings. This is exactly why this forum is so awesome, helping those that care about the gory details sift through all of the evidence and determine what is best for their car. The copies of original drawings are indeed a great source, but are not always “correct” from a thoroughbred context.