Hello Philip, welcome to myBulova. Most of us agree that an heirloom watch from a father or in your case a grandfather is a very special thing. I looks like your grandfather took very good care of his watch, congratulations. Accuquartz followed Accutron so it's almost the third generation of the Accutron line for Bulova. These watches (the quartz version) were first produced around 1974 so I suspect it's a little newer than you thought. I can't quite make out the lower line you refer to but i don't think it's a part of the serial numberor a date code, I'm not sure what it is. These watches were considered state of the art at the time but alas the quartz movement almost became the end of mechanical movement watches.
I think we'll tag your watch as an Accuquartz but without opening the case and getting a date code from the case back or movement we may not be able to ascertain the year of manufacture. I would suggest 1974-75-ish, Thanks for sharing it, you're very fortunate to have it!