Brock akafambisawo Holden Monaro 427C yeGarry Rogers Motorsport (GRM), achikunda makwikwi mana kubva pamakwikwi mana mune izvo zvaifungidzirwa kuti ndezvekuratidzira mumakwikwi ekutsigira e2003 Australian Grand Prix
MuMelbourne. Izvi zvakamutungamira kutyaira 2nd Monaro yakavakwa uye inomhanya neGRM muAustralia Nations Cup Championship, GT-mhando yemakwikwi emota dzakagadziridzwa zvakanyanya uye dzekunze mumugwagwa muna 2003 asati amisa timu yake yega iye nemwanakomana wake James muna 2004 (naMonaros yakapihwa neGRM). Akawana gumi Bathurst kutsungirira kukunda muna 2003 paBathurst 24 Hour, paakakunda, naGreg Murphy, Jason Bright naTodd Kelly muGRM Monaro yake, zvine nharo inofambiswa ne7.0L 427 cui V8 injini pane 5.7L Gen III yakashandiswa nekugadzirwa kweMonaro CV8 (nharo yakabva kune imwe motokari muNations Cup ichikwanisa kumhanya injini yakasiyana nehukuru kubva pane chigadzirwa chekugadzira icho chaive chakavakirwa. Mutambi weTriple Nations Cup Jim Richards akatumidza Monaro se "Better V8 Supercar" apo yakatanga kuonekwa pa2002 Bathurst 24 Hour).