David,

While it is not a normal GA-122 it could be a conversion.
AT&SF liked to kit bash configurations. I have no
information on a GA-123 class. It appears to me that if
the body of a GA-122 was mounted on a flat car this is
what you would have.

The only longitudinal hoppers I can find at this moment
are AT&SF 77995-77999 which were built by Baldwin-Lima-
Hamilton in 1963. They are ore cars set rather high above
end frames with long lengthwise doors. Show as being used
at Hillside AZ. My first guess would be some kind of copper
ore concentrate. I'm sure the door configuration matched
what the customer had for an unloading area. That car series
was classed as GA-132.

These were not ballast cars. I do not think the doors had
any available adjustment, they were either open or closed.

Russ Strodtz