Using measurements taken from the case and appropriate images of original A22 backs, I arrived at a full sized paper template for marking out some 3/16" mdf board.

The mdf was cut, drilled and smoothed until I was happy with the finish, then given a coat of acrylic matt black paint.

I made up some graphics again from images of original A22 backs, carefully cut them out, and glued them on in the correct places.

The entire back was then given a couple of coats of acrylic clear satin lacquer - this sealed the graphics and gave the back a similar textured finish to that of an original.