Hmm... what could this be?

I'm not a newb, and fully appreciate this watch is a total gamble. I know the dial is likely not in nice shape under this very scratched and murky crystal. I know this means the movement could have moisture issues. I know it's only 33mm, albeit a thin case. I know the crown is not original. Etc. Etc. Etc. What I can say, is in my opinion it's legit Omega and not a fake, just a well weathered watch needing some TLC.

What I don't know, because of the very plain dial, lack of any movement or caseback shot, and general lack of description on e-bay where I bought it for a ridiculously low price, is:

-What case reference(s) could this be?
-What manual wind movement is likely to lurk within?

My movement guess was initially a 620, but the case and lug profile is all wrong. 620's are usuall in Geneve models with blocky lugs and stick hands. There is clearly no provision for a seconds hand, so maybe an earlier generation of what became the 620? I'm not sure what though.

When it gets here, I'll open it up and see if the guesses here are right or not 😀 I've got pocket money (for me) in this thing, honestly I bought it just because I'm curious and have a soft spot for the manual wind thin watches.

Hi, it could be a cal. 601. The hands seem to be from a different watch, but I'm not an expert.

A 601 would typically have a sweep seconds. There is no provision for on on the pinion here.

Well, you're definitively right!

After a Google that seems likely. If it is one, it has a snap back. I had imagine it might have been a front loader from the photos.

Honestly I had never heard of a 511 movement before today. Seems fairly obscure, though that does appeal to me.

Some more pics now that I have the watch and was able to pop the back off. The crystal is not omega. It's a cheap replacement that is both really beat up, cracked, and also age yellowed. Crown is some generic replacement. The watch case is mercifully not polished, and the inevitable spiedel band lug wear isn;t too bad. The movement is VERY sluggish, but the balance is OK, as is most of the bridge plating. There is some minor surface rust on a few parts that should clean up when it's serviced.

The bad - I can't get a good dial pic to see what it's real condition is under this awful crystal. The crystal has no exposed edge for a crystal lift, you have to remove the bezel to pull the crystal, and even though there is a snap back, it's just there to adjust timing. The movement comes out the front after a bezel pull. Sadly, I don't have a bezel tool 🙁 and will need to bring it in to a real shop. Because of the curvature of the crystal, I can't tell if there is a SWISS MADE or SWISS under 6, or if there ever was one. That said, the OMEGA font looks OK to my eye. What do you guys think? Rough original, or old repaint?

Hands look to be Omega hands, but either they faded or are incorrect rose gold alpha hands.