Hi there! Welcome to the forums.
Your watch has what is called a snapback, or snap-on caseback. These are generally removed with a proper, watch opening knife that slots into the slim gap between caseback, and you gently rotate the blade so the caseback pops off. Sometimes, this is a specific place where the gap is slightly larger, either as part of the original design or because people have had multiple attempts opening it.
For that reason alone, I would suggest getting a professional watchmaker to help you in opening the watch - particularly since the watch looks in good condition, and scratching the caseback and/or inside of the case is a surefire way to decrease the value of the watch. You may also get loose bits from the force applied opening the case into the movement, which is never a great idea.
The caseback and crown appear to be genuine. Here's a couple of pictures of a similar model with the same caseback reference number:
Your watch, then, is most likely to be from 1960-1961 (with the 17 million serial number,) carrying a Cal 268 movement inside, with a redial carrying the correct hands. Would like to see a photo of the movement inside just to confirm the movement calibre and the serial number, either from the seller or a watchmaker who will agree to look inside your watch.
If you like the watch, I would get it serviced by a competent watchmaker to ensure that the movement is properly cleaned and oiled so that you can enjoy wearing the watch for years to come. If you're concerned about the value due to the redial, wear it for a couple of times to see if you and the watch are 'compatible' and if it warrants your time (and servicing costs.) If it doesn't, sell it, as watches are always available and the next is never too far away
😀
Also, as a new member - if you don't find a profile picture, the admins are very cheeky and will give you one brewed straight from a witch's cauldron
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