My comment above that I think there is an error, is wrong. i.e. its correct, even though in real life the pin holding the valve levers to the valve rods is separate to the slipper operating in the curved guides and above it.
Usually, Joy valvegear has a slide fixed to the valve levers just down from the joint with the valve rods. For anyone not familiar with Joy gear, the radius link is fixed to the frames at its front, and as the wheels go round the correcting links and valve levers bob up and down. The weighshaft (marked "curved guide" on the drawing), can be pivoted by the driver using the reversing wheel and reach rod, so that the curved guides are angled forwards or backwards. As the levers all bob up and down and the slipper (not really shown) slides in the curved guides, so the valve rods move forwards or backwards, depending on the angle of the weighshaft and guides.
The drawing shows it in mid-gear.
From a modelling point of view, Joy valvegear gives fast valve movement with no eccentrics (hooray!), but unless the rods and pins are kept small it can all get rather wide, making clearances tight. Also, at its front limit, that pin in the connecting rod is VERY close to the motionplate.
Mike