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There's another more official term for them, but I can't recall it at the moment. And most people seem to call them shark-fin anyway, so that's the best way to search. You can also search by the movement, which is cal 89.
Using "shark-fin" as keyword, I found OF posts about this watch:
https://omegaforums.net/threads/ros...with-shark-fin-lugs-and-period-buckle.108399/
https://omegaforums.net/threads/serving-notice-im-back.76641/
I'm going to be on the lookout for combinations of R521, as well as cal 89 and shark-fin. I love that I'm finding out all these really cool references from forum posts here!