Up until March 1965, they were 10 gal...then, they changed to 12.7 gsl....the 10 gal tank is held on with 2 straps; the 12 gal is bolted through the trunk floor.
Your car, # 40841, is a late 1964 production car.
However, back thwn, dealers titled them when they were 1st sold....so, the dealer that sold yours did so as a new '65 even though it was produced in '64...nothing wrong with that.
Which gas tank do you have (& pray it is the later one!)