About 45 years ago I had the opportunity to take a cruise on the Delta Queen and spent several hours in the engine room watching the lever operated poppet valves and California cut-off valve gear. I started on a model of the engines (I don't have an interest in building a boat), but challenges to building it along other life distractions got in the way. Last year I started again.
I am only aware of two or three of the lever style of engine that have been modeled. One was a beautiful close scale model that was displayed at a Model Engineer Exhibition in the U.K. in the late 1970s. Another was a working model that was designed for function rather than appearance by Sam Hodgeson. A very complete set of drawings was advertised in Live Steam in the late 1970s and I believe they are still available. The third is a well done steamboat with working engines. A Youtube video shows the engines being tested. This engine doesn't allow variable cut-off, but is reversing.
There is also a build log on the web for a beautiful model the W.T. Preston steamboat with engines, but it uses piston valves. My preference is for the lever action valve gear where everything is out in the open.
Posted are drawings of a couple of examples of engines with lever operated poppet valves. The top one has California cut-off valve gear and the bottom uses three cams for the valve gear. One each for forward and reverse with full stroke steam admission and another that cuts off part way through the stroke for forward only These are what I'm using for general guidance. I'm not modeling any particular engine, but do want to have a good representation of what they look like and how they operate.
The aluminum plate and grey 3D printed cylinder in the third photo are to allow me to mock up some of the valve gear parts.
I've investment cast quite a few of the smaller parts, including the pillow blocks and standards that go on top of the engines and the cross heads.
I had to upscale my casting equipment before I could cast the cylinders and the first (failed) attempt is shown. Both of those are going back into the pot and I will try again to get better castings. These were actually 3D printed in three pieces, each end of the cylinder and the center section. It worked, but took a lot of effort to put the parts together and make sure the seams were filled so there wouldn't be any unwanted voids. Since I printed those I got a bigger printer and for the last few days I have been redrawing them as a single piece.