Can I assume that Mr. Blank of Bendingo, Victoria, Australia is in fact
Charles Casey.  A letter in the Mark Twain Project's archives seems to
indicate that such is the case but does not explicitly say as much.
(To Charles Casey  15 May 1876 • Hartford, Conn.)

and rather than Carrington Castle, the name would be Pollerton Castle,
Carlow, Ireland.

It is interesting that a man would travel from the green of Ireland to
the brown of arid Australia - a man without need to money. Mr Blank is
not described as a gold miner.