Absolutely gorgeous watch with tons of sentimental value! That is a real beauty you've got your hands on, and the fact that it has been passed down as an heirloom from your gramps, to your pops and now to you is really something. It is definitely a valuable watch for sure. I sincerely hope you never sell it... If I were in your shoes and didn't need the funds, with it's family history, it would remain with me forever! Below is a link featuring a similar piece as yours. This may be a bit more valuable because of condition, as well as the yellowish patina (natural aging) on the lume plots, but it should give you an idea of what your watch could be worth.
https://tropicalwatch.com/watches/7wk4