The cast aluminum box will corrode until it is white powder. If they haven't already, the 6-32 screws will corrode to a point where they will be siezed in the threads, and will break off rather than unscrew.
The "brackets" across the front of the box will most likely twist out or just fall apart.
I think that's what 300.6 (B) is about:
"Non-ferrous raceways, cable trays, cablebus, auxiliary gutters, cable armor, boxes,..........embedded or encased in concrete or in direct contact with the earth shall be provided with supplementary corrosion protection".
