Is this Ultra-Chron genuine?

Dear watch enthusiasts, can anyone help me check whether this Longines Ultra-Chron is genuine with original parts please?

Caliber: 431 (17 jewels)
Reference: 8309
Size: 34.5mm without crown, 36.5mm with crown, 10mm thick

I found a reference site for comparison: https://www.watchprosite.com/horolo...dinary-chronometer-will-do/17.527406.3206381/
It shows that Cal.431 has 25 jewels, but in my pictures the caliber has only 17 jewels. I found another site that shows a version of Cal. 431 with 17 jewels: https://watchguy.co.uk/service-longines-ultra-chron-calibre-431/. However, the color of the engraved text on the caliber in my pictures looks a bit different to me.

I'd like to ask the opinions from those with discerning eyes. Thank you!

Sure seems like it's maybe two different watches? Side shot with the crown you can see the bezel ring is there and sticking up above the lugs. But in the other shots? Seems to be gone.

Glove shot vs. fabric shot = different watches. I'd say get more photos.

Edit - Front loader so maybe they popped the crystal and took the bezel with it.

Thank you all! Here's another front shot:

Yes, now I see it. I guess in the first picture the bezel ring was removed with the crystal to give a better look of the dial. Thanks a lot for your replies. They are very informative.

I had one exactly like this about 15 years ago. For some reason I sold it. I think I thought it was too thin and light. I marvel at the quality of the movement today. It looks right to me but I couldn't say whether the crown is original.