To better utilise low patronised First Class carriages and to implement carriage set running, the First Class carriages classed _AZ_ were modified with a guards van compartment and reclassed to ACZ.
The compartment modifications include seat, desk, periscope for safeworking observation and emergency brake pipe cock.
The conversion were performed from 1984 to 1990. Some cars from the "Spirit of Progress" train were restored to broad gauge when the train stopped running.
The cars are in the "200" number block. This reflects a renumbering in the early 1980's to clearly identify steel carriages from heritage stock.
Car numbers recorded by the writer are: 251 - 260, 262, though this may not be the complete list.