RE: os 120 fs ???
Most of the pictures are illegible but yes you do have a choke which were dropped quite some time back as they are really not neccessary.
From your description the other line with a cap sounds like a tee for some sort of fueling senario. I would recomend just using a two line system like any trainer.
Does this engine have the pushrods behind the cylinder or in front of the cylinder?
John