This is the less common earlier series with the ivory dials. Although this one seems to have made a trip to the Rolex service center and got 'fixed'. Nevertheless, it is a solid 16550, and one of the most undervalued sports rolex today. I just am not into white dialed watches. Slightly off white dial, nicely yellowing tritium markers and hands. Head only. Serial is 89921xx I like Speedmasters, JLC, IWC, Issued Military, and Chronos.
Lovely looking watch. I think the hands may have been replaced also, as the 16550 had silver hands. Black hands on the 16570.