Stephen's model is as near scale as is possible with standard parts and driven by a crane motor. The motor drives a primary crankshaft which operates the pistons, therefore driving the coupled wheels via connecting rods. This is the first time I have seen this done, usually the wheels are driven and the pistons dummy. The slide bars are unique whereby a narrow strip overlaid by standard strips slides in the space between the slotted holes of two AG‘s spaced apart by a 1 1/2” strip.
Alf Reeve has started on an SML dragline and is adapting the 1929 steam engine to drive it.