9" or 10" drums...?

My 68 barracuda has a 318 with 10 inch brakes drums front and rear and 7 1/4 rear end.
That year the 6's came standard with 9 inch drum all around.
The v8s came with standard 10in. all around. Both having discs up front had 10 in. drums in the back according to the sales info pamphlet.