Identifying Grandfathers Seamaster

Hello,

Very nice heirloom.
You need to search the forum for a recommended watchmaker in your area to perform:
-movement service only;
-crystal polish; keeping existing crystal if original;
-NO touching of dial;
-NO case polishing at all; use of polishing machines to be forbidden at all cost as they would remove too much material especially from the edges of your case.

This is a collectible watch which is why you shd not trust a local jeweler or just any watchmaker.
Those jewelers use watchmakers who cater to lay persons, and try to make old watches look shiny and new. Thereby ruining the collectible character of the watch, and often damaging it (with excessive cleaning or polishing).

Straps are a matter of taste. If you want to wear your watch on a regular basis in a casual style, which you can, I would wear it with a flat grained calf strap, suede, or matte croc.
Important to avoid stitches or at least no contrast stitches as they would look too busy or clash.

Colors brown, honey, navy blue, oxblood, or dark forest green, dark olive or khaki green.

Many good suggestions below:
https://omegaforums.net/threads/strap-suggestions.163333/