Re: Starting another build
I haven't seen the engine yet but in your pictures it looks like it would be possible to fit a plastic timing chain tensioner shoe into the case. With one end toward the driven sprocket hinged and a coil spring located somewhere near the center of the shoe to hold it lightly against the chain. Alternatively one could hinge the shoe and have a locked screw mounted through the edge of the case which would adjust the slack by pushing up on the shoe. You really don't need much pressure, just enough to keep the chain from slapping. Systems like that are in lots of auto engines to control the slack in timing chains.
Goldwing 1500, Silverwing 600, Schwinn 49