Thanks all. It seems to be 1971 Omega Seamaster Chronograph Automatic ref. 176.0001. Seems to be rare, and omegas first automatic. Learned a lot reading about it.
The applied metal markers for each 5 minutes would make it a yachting type dial, type “I1” per the calibre1040 website. Since the OPs example doesn’t have the yachting bezel, however, it’s possible that it was replaced during service or it’s a made-up watch. The case style for the OPs watch does not conform to the 176.010 yachting case either, looking more like the 176.007. Again, per the calibre1040 site, a type “I” dial is acceptable in a 176.007 case, albeit less usual. In any event it’s a nice combination. A new crystal would surely help. Photos of the interior of the caseback would also help the identification.
It’s a 176.007, which is not at all rare. Some early 176.007 were also stamped with 176.001 crossed out. 176.001 (or 176.0001) was a totally different watch. It was less common. The dial is most associated with yet another model, ref. 176.010, the “Yachting “ Seamaster. Although there are several examples of 176.007s (and 176.005s) seen with this dial that appear to be original, so it may have been an option on the 176.007. Edit: Forgot to mention, very few c.1040s were actually made in 1971, most were made from 1972 through 1976.