grandfather's watch. Insight needed please

The watch is quite nice with the original facets and lines of the case still visible. Often these get heavily polished which makes the case look blobby and the lugs like bent sticks. Please don't polish the case, the watch looks great! The crystal can be polished to remove scratches without adversely affecting the value. As @Asturianucu says, all the identifying info is on the inside, but don't try to open it unless you know what you are doing. Are you in the UK? If so, you can find good watchmaker recommendations here:

https://omegaforums.net/threads/looking-for-a-uk-watchmaker.133557/

It's beautiful.

Sorry, that's all I got.

Much is now known but this question above once answered will determine the value since a genuine removable Omega bracelet is worth rather more than a soldered on aftermarket one which would need very specialist work to remove or resize. A photo of the back and clasp should be enough to clarify all.

Here is your watch in a UK catalog from 1967:




http://www.old-omegas.com/cat67en.html

gatorcpa

Stunning watch and in beautiful condition. As others have advised, it likely needs to be serviced and you must be very careful in selecting an independent watchmaker with an Omega parts account who has considerable experience servicing vintage watches. Whatever you do, don't send it to Omega for servicing. If you tell us where you're located, we can likely provide you with some names of independent watchmakers who can properly service the watch and preserve its vintage character.

That's quite nice!
Helps that you actually took a good picture of it too.

Omega will replace many parts to bring it up to their service standards and in doing so may negatively impact the value of a vintage watch, in the view of most collectors. In addition, Omega will keep the watch for months and will be very expensive. If you can find an independent watchmaker with Omega parts account, they are usually more sensitive to the wishes of vintage watch collectors and can service the watch while preserving the appeal and value of a vintage watch. You can ask for a service plan and quote outlining what the watchmaker suggests and post it here for advice and input from very experienced collectors who have already commented on your watch and will be available to help you through the process.

As noted above, the confusion with the Old Omegas image is that the OP watch is a dog leg and the model shown in the brochure with the similar bracelet is a curved lug model. Note the leading 5 in two of the model numbers listed there. This indicates UK production. Based on the date, the curved lug catalogue watch with the OP bracelet are likely DS&S (Shackman & Sons) rather than Dennison production since the latter were defunct by the mid 60s. It is just possible that the OP watch is early enough to be a Dennison model but I doubt it. Shackman made some lovely bracelets (not sure Dennison made any in fact) so even if not Swiss it is still high quality. There is the real possibility though that it is soldered on to the head which is a big negative since obviously it can't be easily removed, indeed removal without professional skill can lead to damage to otherwise very nice lugs. Bracelets like this often have very little adjustment, also an issue with resale value, though not an issue if it fits correctly and resale is of no import.