Hi Jeff,
These are just the single vehicles that I have seen with the early-style valve covers that have the latest dates listed on the door tag (projected date). They are merely points of data...
I should have noted that these three cars were claimed to be unrestored as well. Yes, it is always possible that these cars were originally equipped with the “Powered by Ford” (PbF) valve covers, and then at some point, they were replaced with the early-style covers. However, given the rarity and obscurity of the early-style covers, versus the relative ease of buying brand new PbF covers, I don’t see why anybody (let alone three people) would go to the trouble of doing that – the swap usually goes the other way around...
I too have seen the PbF covers on cars with earlier build dates, but unfortunately, all of the examples of Sept./Oct. cars with PbF covers that I have photos for were of restored cars, so unfortunately, I can’t really rely on them as “proof” of the earliest example of PbF cover usage...
Question for you - are the three October cars you listed below (7R1159xx, 7R1229xx, and 7R1288xx) examples of original/unrestored cars with the PbF valve covers?
Looking though my documentation, I think we could safely say that most (if not all) of the 390 cars built prior to October 1, 1966 came with the early-style valve covers, and then the transition began to take place sometime after that date. Does your data agree with this assertion?