GPM (VEB Geräte und Pumpenbau, Merbelsrod) is an East German company who's main line of business is (I believe) car parts and/or pumping equipment. That's about the limit of my knowledge of this company so I don't even know if this is their only steam toy. It is similar, in many respects, to Wilesco in look and feel and, no doubt, that was a source of inspiration when they were at the design stage.
It's a solid looking engine, let down by the use of steel in the boiler and other water-side parts, and plastic in some small parts like the pulley, throttle knob and burner handle. The boiler is 58mm diameter by approx 155mm long (including a domed end and the Wilesco style circular sight glass). It appears to be cast in one piece (apart from the fittings), though this could be an illusion. The burner is a solid fuel tablet type, almost a direct copy of Wilesco practice, even including the adjustable air holes. The combined safety valve / whistle, pressure gauge and water sight glass are also similar to Wilesco's.
Steam is fed from the top of the boiler via a needle valve throttle to the cylinder. It has a double-acting cylinder, 14mm bore x 16mm stroke, utilising a "piston" valve driven off a slip eccentric for reversible running, all similar to Wilesco. There is a lubrication point in the top of the valve chest. Exhaust is fed through a short pipe to a drip tray, unfortunately missing in this case.
Con-rod and valve linkage are, also, almost a direct copy of Wilesco. The crankshaft has a generous 81mm diameter flywheel and a small pulley. The chimney is purely decorative; not even the steam exhaust goes up it.
This engine was in almost mint condition when acquired and I don't think it had ever been fired prior to my purchase (it has now!). It runs very well and turns over at a very low 0.1 bar on the gauge. Considering that the gauge is marked up to 2.5 bar and has a red line at 1.5 bar, this is admirable.