Heres some pics of the American Turbine and Berkeley 12-JG pump housings side by side.
To the left is the AT pump, the right is a JG

Opposite on this one, the left is the JG berk.

Bowl side, the AT is on the right, JG on the left

Finally, should be self explanatory by now, AT on the left, JG on the right, Intake side.

Not any appreciable difference that I can detect without a machinsts table and a dial inticator stand. Look similar enough for most of us!
Ray