Firrito, who trained as 'keeper along with Drew Petrie and Jared Brennan, was named in a back pocket.
Australia coach Mick Malthouse said after an extensive workout on Thursday morning Bock was the standout choice.
"We've hit him with everything," Malthouse told a packed Perth press conference on Thursday afternoon.
"He's agile, knows the game, [is] willing, brave and no doubt they'll test him out.
"It's a strange position that's probably the only one on the ground that is totally different to anything we see in AFL."
An expanded ten-man bench was named, with one player set to be omitted before the Test gets underway.
GK: Nathan Bock
B: Michael Firrito, Brad Sewell, Campbell Brown
HB: Ryan Crowley, Drew Petrie, Adam Selwood
M: Brent Harvey, Scott Thompson
HF: Scott Pendlebury, Daniel Motlop, David Rodan
F: Michael Osborne, Shaun Burgoyne, Matt Campbell
I/C (one to be omitted): Matthew Boyd, Jared Brennan, Nathan Foley, Roger Hayden, Leigh Montagna, Marc Murphy, Max Rooke, Kade Simpson, Dale Thomas, Daniel Wells
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The 2008 Toyota International Rules Series: Australia v Ireland
First Test – Subiaco, Perth, Friday 24 October
Second Test – MCG, Melbourne, Friday 31 October
Tickets on sale now at ticketmaster.com.au, by calling 1300 136 122 or at a Ticketmaster outlet.
For full coverage of the 2008 series, click here.
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