8 1/4" on an Early A, What wheels are you using?

measuring to the backing plate is not accurate because of the differences in the backing plate dimensions. some backing plates had "offset" to account for various brake setups, ie; different width and diameter drums. Note that most 7 1/4 rears had narrow brake shoes and the 8 1/4 had wider brake shoes. I would measure to the axle mounting flange to get a more correct idea of what your dealing with.