My son bought me this beauty for my 50th (1968-2018). Believe it or not it's my first Accutron.
Popped a new '344' battery in it and replaced a missing screw and she fired right up and has been keeping amazing time for the last few days.
Watch came with original box and booklet showing the model as a '21364' which is confirmed in the advert below. No variant model number found so far.
Inside case is stamped '741'.
What I also like about this particular watch is that it has all three branding elements on it: the Tuning Fork, BULOVA and ACCUTRON.
1968 Bulova Accutron Calendar (21364)