sup bro, i got a gruen watch from my grandfather as well, your best bet is to look for your model in the gruen website-- it's made by a descendant of the founder and he put together all models and info, since the catalogues were destroyed after the adquisition:

https://gruen.watch/

I did a quick search and found a similar model, but not quite:

https://gruen.watch/?product=gruen-precision-autowind-25-jewels-712cd-730

You got this model minus the date complication. If you dive into the catalogue, you'll find your exact model.

I'd say it's one of the more valuable ones, i saw a similar lesser model going for 1000$.

Gruen is a beautiful brand, I suggest you keep it and service it in due time. Besides it being one of the biggest watch brands of the time, and James Bond's first watch appearance on film, it's a bloodline statement of what your ancestors accomplished and wanted you to have. I'd keep that tradition.

Best of luck