Oooh, very nice! Is it a 7951 or an 8301? You can tell from the caseback - if it opens with slots it's a 7951, if it has a 12-sided edge it's an 8301.
I'm a little bit obsessed with these particular references, I did some blog posts on them:
https://www.moonagewatches.com/post/the-longines-ultra-chron-jumbo-models-part-1-the-great-sleepers