Typically 11 x 2 on the rear when equipped with 2 & 3/4" front. 11 x 3 all around were available for taxi/police spec cars. I don't believe there were rear drums in sizes between 11 x 2 and 3 " but I could be wrong.
My 68 Convertible has 2 3/4" rear shoes with finned rear drums (the fronts were also 2 3/4" shoes/drums before they were swapped out for 73 Fury Discs)
CENTRIC 11103360 Premium Brake Shoes-Preferred; Bonded Info FitsRear; 3" Front Shoe; Police Taxi Tow package & HD OrFront; 3" Front Shoe; Police Taxi Tow package & HD OrFront; 3" Front Shoe; Except Police Taxi Tow package & HD
CENTRIC 11204460 Heavy Duty Brake Shoes; Riveted Info Rear; 2-3/4" Front Shoe