drum brake sizes

my 69 RR is supposed to have come 11 inch drum brakes correct? where is that measurement taken? are they actually 10.75? trying to price out drums and wheel cylinders but the assortment of sizes is confusing ! given the cost of shipping I don't want to pay for returns and the NAPA site lists different sizes??
thanks!

According to the dealer data book, brake sizes for a '69 RR;

- standard equipment was drum brakes front and rear, 11x3 front and 11x2.5 rear.
- with optional front disc brakes, the rear brakes were 10x2.5.

Brake sizes are drum diameter (inside) x shoe width. Example; 11x3 brakes would measure 11" inside the drum and 3" wide at the shoe.