……よくもこのような若輩の身でそのようなことが堂々と言えるものだ…。
My guess would be that 身, in this case, means "one's position" or something like this, but how does that really work? For instance, if I were to say アメリカ人の身で in a context where an American wouldn't be appropriate to talk about something, would that work as "Even though he's American..." or "Being American.." (in a negative way)? It reminds me of 身の程知らず.
Additionally, I'd like to know what もの expresses here. Is it something to express a feeling of surprise?