John,
The smokebox/boiler/firebox is partially released by the screw situated between the centre splashers on the underneath of the footplate. However there are two tabs at the front of the rear splashers again underneath, that prevent the whole unit from sliding out.The front of the cab on mine was not secure so I was able to lift the cab front upwards and then lift the fire box up slightly and slide the unit out. This will reveal the faceplate which is stand alone.
The tank front under the boiler will also come out if not glued properly, again it is a slot and tab.
I continued to rock the cab up and down and eventually the cab broke loose, admittedly not at the designed slot and tab but along the moulded coal, so that when the cab is replaced you cannot see the join.
Hope this helps although I cannot accept any responsibility for any mishaps.
Pete