Rear Brake Dilemma

It's hard to tell from the TINY pictures posted on your webpage, but at the very least those are the wrong drums for the backing plates you have. None of those pictures zoom, only the thumbnails actually load.

If I had to hazard a guess, someone did a BBP conversion on your car and used 11" backing plates. But, those backing plates are specific to the size drum they're for. BBP 11" rear drums came in 11x2", 11x2.5", and 11x3", and you CAN NOT mix and match the backing plates and drums between those sets. The BBP axles all have the same flange offset from the housing, so therefore the backing plates do not for the different width brakes.

It's also hard to tell, but if your axles are A-body axles that were re-drilled to 5x4.5" then you still actually have to use SBP brakes, just with the drums re-drilled to 5x4.5. The axle flange offset is different going from SBP to BBP brakes. I don't think that's what's going on because of the diameter of the axle flange in the pictures, but they're small pictures.

Somewhere on here there's a thread that lists the various offsets of the BBP backing plates to identify which ones you have, I'll see if I can find it.