We are very grateful to Roy Hart from Rangoon who gave us this additional information
I would say 1975-6. It had certainly gone by 1980. The box opened 1904 (when the viaducts were completed) and closed 07/07/1925.
When it closed, the operation of the trailing points in the down main was transferred to a 3 lever ground frame next to the building, the windows were permanently boarded and the structure was used by the engineers as a mess and store room.
Hope this helps,
All the very best,