Calling on memory of 60 years ago, so bear with me. Also forgive my lack of proper terminology. There is a ramp in the lower end of 21 which pushes on a plunger 20, which moves clutch dog away from forward gear for neutral. Pulling up on 21 is what causes this to happen. Spring 23 pushes 21 back down when tension on cable is relieved.
I think you are asking about tube #25. It is held down by the tab on the lower water pump cover, but is offset enough for the cable to move up and down. The instructions that Garry posted says to use a pin to hold it down for assembly—-something that I’ve forgotten.
