Seiko 6139-6000 from October of 1969 (happens to be my birth year and month too). Arguably the most common of the Speedtimer 600X cased variants, still not an easy watch to find in good shape as they were all JDM only. These were only made from around March 1969 to early in 1970. All of this particular model 6139 should have a two-piece seconds hand, notch above the crown in the case and the earlier 6139a movement. The Speedtimers received the 21 jewel movement rather than the 17 jewel.