I did not know what to name this assembly. It attaches to the cross head, and pushes the handle of the steam valve up and down each revolution to admit and release steam from each end of the cylinder.
It uses the U shaped metal strip which I cut out and bent yesterday. It is 230mm long, and I made it from brass, including the filler strips which actually contact with the valve lever. I made the filler strips a few mm longer than necessary, so I can file them as necessary when the engine is timed.