The axles are SBP? Well, that's your problem. :banghead:
They never made SBP 11" rear drums. So, you have 11" BBP drums and backing plates that were drilled for SBP. Problem is, as I mentioned above, SBP axles and BBP axles do not have the same flange to housing offset. Which is why you have those "spacers" on your studs.
Yikes. #-o
So, the good news is that you can probably just re-use the brakes you have (without the spacers!) if you buy a set of BBP axles.