The valve gear comes off with the plastic chassis. In fact, it is possible to remove the valve gear with the plastic chassis raised just a little, and it is probably best to do this to avoid any damage to the fragile components. Note that the piston rod and the con rod on both sides are not permanently connected, and will drop off at some point if you are not aware of this. The photo shows the rods splayed out to aid refitting, but it can be seen how the flat cross member slips under the gear housing from this photo.