Just as an FYI, this is almost certainly made in the 2nd half of 1977. Your first 4 digits match mine, and from
https://www.ilovemyspeedmaster.com/productiondateprediction/ it places mine in June of 1977. Interestingly yours also has the long S that almost touches the R in "Professional". If you are willing to share it, I believe
@Foo2rama may be interested in the whole serial, and whether it comes before or after mine, as mine so far has been the earliest example (by serial number) of the long S.
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