Hi Alex.
Unfortunately, you won't find the year the serial number correlates to that way. In 1969 Longines restarted it's serial numbers at 50,000,000 and there's no table from that time on. However, that has a caliber 990 inside a case reference 4394 (the 1 means it's the first version of that model number) which would make it a mid- to late-70's watch.
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