Brock ayaa sidoo kale ku waday Holden Monaro 427C oo loogu talagalay Garry Rogers Motorsport (GRM), isagoo ku guuleystay afar ka mid ah afar tartan oo ah waxa loo maleynayay inuu yahay muuqaal hal mar ah oo ka mid ah tartamada taageerada ee loogu talagalay 2003 Australian Grand Prix
Waxaan ku noolahay Melbourne. Tani waxay keentay inuu kaxeeyo Monaro 2aad oo ay dhistay oo ay maamusho GRM tartanka Australian Nations Cup Championship, oo ah horyaal nooca GT ah oo loogu talagalay gawaarida waddooyinka ee aadka loo habeeyay iyo kuwa qalaad ee 2003 ka hor inta uusan u sameynin kooxdiisa isaga iyo wiilkiisa James 2004 (oo leh Monaros oo ay bixiso GRM). Wuxuu gaadhay guushii tobnaad ee Bathurst ee adkeysiga 2003 ee Bathurst 24 Saacadood, markii uu ku guuleystay, Greg Murphy, Jason Bright iyo Todd Kelly oo ku jiray GRM Monaro, oo muran badan ka dhaliyay 7.0L 427 cui V8 engine halkii uu ka ahaan lahaa 5.7L Gen III sida loo isticmaalo wax soo saarka Monaro CV8 (muranku wuxuu ka yimid baabuur kale oo ku jira Koobka Quruumaha oo awood u leh inuu ku ordo matoor cabir ka duwan kan lagu soo saaray. Horyaalkii Koobka Quruumaha Saddex-geesoodka ah ee Jim Richards ayaa ku tilmaamay Monaro inuu yahay "Better V8 Supercar" markii ugu horreysay ee uu ka soo muuqday Bathurst 2002 24 Saacadood).