I'm inclined to say speedmaster 3113.30.00 https://www.omegawatches.com/watch-omega-speedmaster-date-31133000
I've seen several other results like 3313.30 and 3613.30.00 but they don't show up on the omega website, so..
I think there might be plated versions that have different ref numbers. The 3113 is apparently solid 18k YG.