9" Drum to 10" Drum Upgrade
To upgrade from 9"x2½" drums to 10"x2¼" drums, only the spindle and the hardware attached to it (backing plate to drum) need be swapped. To upgrade 9"x2½" or 10x2.25" drums to the KH 4-piston discs, you'll need spindles and the heavier duty lower ball joints (using the drum brake lower ball joint would probably lead to premature ball joint failure). The 1960 to 1964 models were only offered with drum brakes in the 9"x2½" configuration. The 1965 through 1972 models were offered with both 9"x2½" and 10x2¼" drums.
9"/10" A-Body Drum to B-Body Drum Upgrade
It is possible to use the 11" drums from a B-Body car if the spindle and related brake hardware are used along with the B-Body lower ball joint. However, the larger B-Body upper ball must also be used, which requires the installation of the 1973-1976 upper control arm (UCA). Since B-Body disc brakes are easier to find nowadays than B-Body drum brakes, there really is no point to upgrade to these large drum brakes with the other disc brake options available.
For those interested in learning more about using B-Body drums (or even C-Body drums) in the A-Body vehicle, please visit the MotorTraxx Techline Brake Upgrade page.