. . . but did have a Seiko equivalent for a little while.

[photo credit: Dr No / watch credit: KMII]
Most Omega 'C' models are branded like yours, Thomas - as Constellations. There were Genève and Seamaster Cosmic versions as well, including manual wind and date-less models.
A friend of mine recently inherited a SM Cosmic 'C' with date (cal 610) which was serviced by my watchmaker, but sold off almost immediately afterwards. Had I known Ray was going to sell it on eBay, I would've gladly taken it off his hands.
Usually hesitant to use the word 'iconic', but in this case, Omega's 'C' cases were icons of their generation.
Thanks for sharing, Thomas!
Best,
Art