A Frankenstein Omega 342

I've bought an old 9ct gold gents automatic Omega at auction in a job lot & would be grateful for any information on it please . It's stamped 9ct on the out side of the case . On the case back it's stamped 12308 Dennison 9ct ALD 299640 . On the bumper ? it says Omega watch co . It has the Omega mark & 342 . Also on the workings 11409460 . The front isn't glass it's plastic , cracked in 2 places & a lot of surface scratches . I say Frankenstein because I don't think the gold back dates to the workings & it doesn't have Omega on the face which is in poor condition . It's running & was gaining 5 minutes a day so I adjusted it back a bit but too much so I altered it again & for the week I kept it running it was keeping the right time . It has a second hand which sweeps rather than ticks . There's some jewelers marks but have no idea what they mean . It could have been owned by someone in the police force as other things in the lot were police related . I wondered if that's why it doesn't have Omega on the face ? It approx 32mm across . It's not a gold winder , only plate & it's rubbed off on the top . There's no Omega mark on the winder . Any idea of its value , age , rarity etc ? The back is dented & the case is scratched as well . All in all a poor condition example unfortunately .

This watch has no collector value. I would sell the case, movement and dial separately for parts.

Thanks for your advice . Is it an Omega face & does the case match the workings please

Thanks very much for your reply . I know a lot more now .