On September 18th, I purchased the catalogs and magazines referenced in the mailbox design patent filings (discussed in prior blog). Yes, ebay is amazing!
I paid a premium for the Sears Fall & Winter 1975 catalog as it happened to have a famous photograph in the men’s section. I still remember the uproar that it caused during a large family get-together back in 1975! I bought the catalog because it was referenced in a unique mailbox design patent assigned to Jackes-Evans Manufacturing Company (No. 851,540). Aside: the patented mailbox was not in the catalog. Oh well. 
To my surprise, a mailbox similar to the mailbox design that is my inspiration was included in the Sears catalog! [mailbox 12]
Another interesting design patent (No. 850,662) referenced the 1974 Montgomery Ward Fall & Winter Catalog (mailbox 15). Again, to my surprise the mailbox design that is my inspiration was shown too! [mailbox 10]
With these catalogs, I was able to trace the general design back to the mid-70s.
Getting closer to mid-century!
mid-century modern mailbox 