I m studying that text too, but I dont have soft copies of my class notes (they were stuff written in class).
Some quick brief points on aspects of growth & transition:
Notice the names: Billy and Old Bill, it is actually a hint of a "furturistic billy" could possibly turn out into a "nohoper" (mentioned at the beginning by billy). This is suggested from the poem "before my time" when billy is getting nightmares. So this suggests a little about transition of what billy may become.
If we draw a general picture of the story:
"Nowheresville" --> freight train --> Bendarat
(now go down another level)
Billy's abusive home --> Bendarat Hilton (train yard) --> Old Bill's home
Billy sets off his journey "leaving nowheresville" then gets on the train to reach Bendarat.
However he doesn't live in "Bendarat", instead he lives in a old train yard where most of the story/events takes place. This kind of suggests that Billy is still on a transition (train & tracks = sense of movement/transition) in his journey until he was finally accepted into the community of Bendarat by Old Bill offering his house to Billy. You can also extract some meanings of growth in the passage.
Sorry I know this isn't very clear since I aint very familiar with the text myself but it will give u a starting point I think
