rear drum brakes issue

the rear has a 2-1/2" brake assembly. backing plates, shoes / hardware, and drums. From reading above, I cannot simply put 1-3/4 shoes on the 2-1/2 backing plates / drums / hardware I have.

is the problem the axles have the incorrect axle offset / brake gap for the 2-1/2 brake package (B-body)? I remember there being two axle offsets. 2.36 and 2.50.
Is the 2.36 for the 1-3/4" brake shoes / A body and the 2.50 for the 2-1/2" brake shoes / B-body

I'm thinking the previous owner ordered axles for a A-body (thinking it was getting A body drum brakes) ........but bought a B body brake assemblies.

or

does it just have incorrect backing plates for the 2-1/2 brake package?

please school me.