indent There is little difference between the early members of the 57xx class and the later variants, sometimes called the 87xx class.  Naturally when a class of engines is built over a number of years some variation is bound to occur but the only difference which is immediately obvious is that the early versions had this single arc-roofed cab whereas the later ones had rounded corners between the cab-side and the roof - an amendment which allowed much larger cab windows back and front.  There were also a few minor variations, such as the position of the front cab step which was moved nearly a foot further back in the later engines while there were other differences between certain members of the class - as always, study photos of the real thing to see what you can spot!
indent This engine is used on the passenger services not covered by our next model, the railcar.  Naturally one could use a completely different type of engine but Panniers generally were far and away the most numerous of the GWR tank engines and a line which used them for one service often used other variations of the type for most, if not all, of the other services - a fact which is probably what led the one-time editor of RM when offering his opinion on engine choice for GW model railways to famously state, "If in doubt, add another Pannier"!