> So the term "guy" became genericized, beginning in Australia it seems, to refer to a grubby lower-class Catholic boy.

I'm sceptical of this alleged Australian connection. As far as I'm aware, the term started in England, spread to the US, and it is in the US that its usage really took off. In Australia, "guy"/"guys" as a term for a male or gender-neutral person was imported from the US in the second half of the 20th century.