(Perhaps belaboring the point, but)

I don't get an entry for "stange" meaning "perch" in thefreedictionary.com, my first goto source for words, only a town in Norway. So I'm confused as to what you mean.

Checked some German and French translation sites. Nothing.

The peculiar thing is that "rail" and "stang" are both monosyllabic and thus work equally well in terms of prosody.

Surely VN would have considered a common word like "rail"; thus must of really intended "stang".

Perhaps VN thought the word sounded bright and ringing, suggesting "steel" and "tang", and thus appropriate to the context.