Dinesh,
I don't know much about the backing plate design on the 2A, however when I look in the Universal Jeep Service manual I see that there are 2 graphics show, one where the hub is outside of the drum as in the 2A and one where the hub is inside the drum, however the backing plates look the same. But the manual does not clearly define which is which.
I just recently completed a brake job on my rears on my 3A, I decide to change to the 3B drums as they completely encase the hub and brakes, I like that design, I did not change the backing plates from the originals and I have had no problems. So all that said, perhaps is doesn't matter.
