Looks like what somebody did was redrill B body drums to the A body pattern. That's why they had to put the washers in. The B body backin plates have a different offset. You probably need to find some A body drums and you'll be good.
That is the reason I asked about the brake shoe width. The picture is hard to tell for sure but the shoes look wider than the 1 3/4" that the a body uses. The self adjuster pictured didn't start until 1969 but will work as a retrofit if you use all the parts.
The big problem is that the rear 10" brake drums that the car would have come with are no longer available at the parts stores.
