Very interesting (as Arte Johnson would say, in his best German accent)! The serial number appears to have a KI prefix, which would indicate 1979, but the frame appears to be earlier and I would have expected a KS prefix. Based on the fork crown, it looks like a Professional. An overall photo and photo of the seat lug/stay attachment would provide confirmation. This is a case where I would be very interested in getting some date codes from the derailleurs and crankarms, as the bicycle looks circa 1973-1974.