This is why I recommend people buy backing plates and drums together from the same car. The backing plates for the a-body 10x1.75 and b-body 10x2 are about the same (or so I've been told), but for a 2.5" wide shoe the backing plate is not the same. The axles come in two offsets, a-body and everything else. Don't buy big bolt axles with a-body offset as you won't find drums that will fit properly.