Victory in the second Test at the Etihad Stadium on Saturday will clinch the series for Robbie Deans' side and he hopes to get a clean bill of health for Waratahs tight head prop Sekope Kepu to ensure he can field exactly the same XV.
Kepu strained a tendon in his forearm in Brisbane and will undergo a fitness test before the weekend.
Kurtley Beale hasn't recovered from his shoulder injury in time to contest for a squad place so Deans has also stuck with the same seven replacements from the opening rubber.
Meanwhile, North and Williams are hoping to return to full training on Thursday after the Welsh side has moved on to Melbourne.
Both players have been receiving treatment for their injuries - North suffered a dead leg and left the field in the first half last weekend, while Williams was helped off after suffering facial injuries in a heavy clash with Wallaby hooker Tatafu Polota-Nau - and North went to training with the non-playing squad on Monday afternoon.
Williams is due to return to training on Thursday after all players get a day off on Wednesday. Howley described them as "minor injuries" and is confident they will be available for selection for Saturday's vital fixture.
Whatever happens, Wales won't be able to follow Deans' lead and field exactly the same side. No8 Toby Faletau has been ruled out of the tour with a broken bone in his hand and former Wales captain Ryan Jones looks set to step into his shoes.
Ospreys lock Ian Evans, who played in every minute of every game in the recent Grand Slam, is included among the replacements for the midweek fixture after arriving in Australia straight from his wedding on a Greek Island on Friday. If he shows no ill effects of jet lag then he could return to the second row in Melbourne.
Australia (v Wales): Adam Ashley-Cooper; Cooper Vuna, Rob Horne, Pat McCabe, Digby Ioane; Berrick Barnes, Will Genia; Benn Robinson, Tatafu Polata Nau, Sekope Kepu, Rob Simmons, Nathan Sharpe, Scott Higginbotham, David Pocock (captain), Wycliff Palu
Replacements: Stephen Moore, Ben Alexander, Dave Dennis, Michael Hooper, Nic White, Anthony Faingaa, Mike Harris