The big tube is the thermosyphon. Kinda like a normal HX in a pump machine except it is fed via a small hole below the water line. Pump machine HX's are fed from fresh rather than boiler water.
The top fitting on Timo's pic is the group feed and beneath that is the return. I have not disassembled the group yet but assume that it has a passive circulation system to keep the group hot. A few of my machines have HX. They are a later feature although not all makers used them. For instance, I don't think the modern astoria group uses one (I welcome correction though

).
I am not convinced about the merits of an 'open' hx (thermosyphon) vs straight boiler fed system in lever machines with regards to thermostability. I suppose they provide a little insulation from cooling during refilling. A passive circulation system is probably necessary here though as the group is not bolted to the boiler.
The boiler and frame (I think) are standard e61 components. By 'e61' I mean the model of faema machine, not now ubiquitous group or copies thereof. The frame has a footprint of 345 x 360mm. This is a little smaller than the conti empress of 350 x 390mm although the conti contains its bodywork to this diamension. The lambro boiler overhangs the rear of the frame somewhat (see other Paul's pic).