This is the earlier Curtiss Model K engine. Working with the fully controlled lifter assembly (Desmodromic) It is using the same rocker to facilitate the exhaust / Intake opening. Very simple and interesting. Thinking! Could this be linked with a Stephenson linkage running at half crankshaft speed and be used as a throttle by varying valve lift and cutoff. Many drawbacks of course from an ideal valve timing aspect. Still interesting though!