This is the back side of the chain case. Fixed piston would be at 9 o clock looking straight on. Kinda clever design to kill a lot of birds with one stone but poorly executed.
This is the engine, how can you not love this, it's basically a 340cc dual av7 with a CVT. Free air cooled even, peak of Fuji heavy industries small engine tech in 1974. I think it does about 20-25 hp. Which is plenty in this 250# machine with like 2" suspension travel