With Emmanuelβs able and scholarly assistance, I just scored a Ref. 43999, the Grand Seiko Self-Dater, from 1964. It is from the 57 GS Series. I donβt have it in hand yet, but hereβs a pic or two or four from the ad.
These vintage Grand Seikos are certainly ageless and timeless classics.
Love your high-beat example KM.