Interesting catch! I like the 321 seamasters. Initial thought was ck2907, but the lugs don’t fit the style, the ck2907 has more rounded lugs. The hands definitely fit the era of ck/ko2907, so I‘d go with mid-late 50‘s.
I hate to ask, but, where is he Tachymeter scale on the dial? I would expect it to be on there.
Take a look at this great thread, some very nice 321‘s seamasters in there and maybe more information for you.
https://omegaforums.net/threads/not-all-321s-are-speedmasters.22332/
Cheers,
Max
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