The only 10" drums with the 4 1/2" bolt pattern used on A body cars were the rear drums. All 4 1/2 bolt pattern front brakes were disc brakes.

The 9" 4 wheel drum brakes used on A body cars are all 4" bolt pattern. These 4" bolt pattern 9" 4 wheel drums were available up to the end of the A body production in 1976. The upper ball joints have different size studs between the disc brake A body cars and all the front drum A body cars. Gene