Pari gbolohun ti o tẹle: Brock tun wakọ Holden Monaro 427C fun Garry Rogers Motorsport (GRM), ti o ṣẹgun mẹrin lati awọn ere-ije mẹrin ni ohun ti a ro pe o jẹ ifarahan kan ninu awọn ere-ije atilẹyin fun
2003 Australian Grand Prix ní Melbourne. Eyi mu ki o wakọ Monaro keji ti a ṣe ati ṣiṣe nipasẹ GRM ni Australian Nations Cup Championship, idije GT-type fun awọn ọkọ ayọkẹlẹ opopona ti a ṣe atunṣe pupọ ati awọn ọkọ ayọkẹlẹ ti o yatọ ni ọdun 2003 ṣaaju ki o to ṣeto ẹgbẹ tirẹ fun ara rẹ ati ọmọ James ni ọdun 2004 (pẹlu Monaros ti a pese nipasẹ GRM). O se aseyori kan kẹwa Bathurst ìfaradà win ni 2003 ni awọn Bathurst 24 wakati, nigbati o bori, pẹlu Greg Murphy, Jason Bright ati Todd Kelly ninu rẹ GRM Monaro, controversially powered nipa a 7.0L 427 cui V8 engine dipo ju awọn 5.7L Gen III bi lo nipa awọn iṣelọpọ Monaro CV8 (awọn ariyanjiyan wá lati ko si miiran ọkọ ayọkẹlẹ ni Nations Cup ni anfani lati ṣiṣe kan ti o yatọ si iwọn engine lati awọn iṣelọpọ awoṣe ti o ti da lori. Aṣejere ife ẹyẹ Nations Nations mẹta Jim Richards pe Monaro ni "Better V8 Supercar" nigba ti o kọkọ farahan ni 2002 Bathurst 24 Hour).