Who were the 'pros from Dover'?

According to Phrases.org.uk, the term originated in the book M*A*S*H, and was used again in the movie. In the book, Hawkeye would claim to be a pro (golfer) from Dover (in a variety of states) in order to be offered free play at a variety of golf courses; the line was used later on in the book, in a surgical setting, to demand more up-to-date information about a patient.

In the movie, the secondary plot about free golfing was not included, but the surgical scene was.

The problem with these postings is that they all refer to a 1968 origin from MASH. However, my grandfather was a senior aeronautical engineer working for Kelly Johnson during WWII and the Korean War in Burbank, CA. He would tell stories about material suppliers and parts vendors who would "send in the pro from dover" when they hit a technical snag....specifically he was referring to a material problem on the SR-71 prototype 'Ox-Cart' between 1948 and the mid-50's.