This is a front Loading movement so you’ll have to split the bezel crystal off the case
Also believe it’s got a split stem which separates under pressure
Hallmarks will be on the inside of the back cover
Not recommended attempting if an amateur
If it’s 18k solid gold that’s Good price tho needs to be confirmed with the other hallmarks inside the case , and if you’re happy with the dial not being original ?
Bear in mind it could be 14k or even (less likely) 9K rather than the assumed 18K. And also bear in mind these monocoque cases are lighter than the traditional kind so the gold value will be less.
I worked on a seamaster DeVille with a similar case design before . I was interested in the watch because of the Price. I think it should be possible to find a good original dial for this Model.